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排序方式: 共有607条查询结果,搜索用时 31 毫秒
51.
Shuya. Wei Xiaoyang. Fang Xuejun. Cao Manfred Schreiner 《Journal of Analytical and Applied Pyrolysis》2011,91(1):147-153
Chinese ink stick has a long history and a special importance in Chinese culture. Its main components are soot (normally pine wood soot and lamp soot) and animal glue; however, additives were added from time to time for different purposes. In order to see whether the two types of soot can be differentiated and the other constituents in Chinese ink sticks can be identified or not by Pyrolysis-Gas Chromatography-Mass Spectrometry (Py-GC-MS) and GC-MS techniques, an initial study has been carried out. The main polycyclic aromatic hydrocarbons (PAHs) in soot could be identified, which are anthracene, fluoranthene, triphenylene and benz[e]acephenanthrylene. The main difference between those two types of soot is that the detectable amount of PAHs in lamp soot is much lower than in pine wood soot. In addition to this, the relative concentration of the main polycyclic aromatic hydrocarbons including anthracene, fluoranthene, pyrene, triphenylene and its isomer, benzo[k]fluoranthene and its isomers are different in the two types of soot. The relative content of benzo[k]fluoranthene is higher in pine soot than in lamp soot, which could be used to as a criterion to differentiate the two types of soot. Py-GC-MS technique is a very effective method to identify the main components of Chinese ink sticks, including the PAHs of soot, binding media and the additives of camphor and borneol in one analysis. 相似文献
52.
In this paper, the interaction between herbacetin and BSA was investigated by fluorescence and three-dimensional fluorescence spectroscopy under simulated physiological conditions. It was proved that the fluorescence quenching of BSA by herbacetin was mainly the result of the formation of a herbacetin–BSA complex. The modified Stern–Volmer quenching constant and the corresponding thermodynamic parameters ΔH 0, ΔG 0 and ΔS 0 were calculated at different temperatures. The results indicated that electrostatic interactions were the predominant intermolecular forces in stabilizing the complex. The distance r=3.23 nm between the donor (BSA) and acceptor (herbacetin) was obtained according to Förster’s nonradioactive energy transfer theory. The synchronous fluorescence and three-dimensional fluorescence spectra results showed that the hydrophobity of amino acid residues increased in the presence of herbacetin. These results revealed that the microenvironment and conformation of BSA changed during the binding reaction. 相似文献
53.
Yasuda M Nakajima H Takeda R Yoshioka S Yamasaki S Chiba K Baba A 《Chemistry (Weinheim an der Bergstrasse, Germany)》2011,17(14):3856-3867
Boron complexes that contain new tridentate ligands, tris(o‐oxyaryl)methanes and ‐silanes, were prepared. These complexes had a cage‐shaped structure around a boron center and showed higher Lewis acidity and catalytic activity than open‐shaped boron compounds. The cage‐shaped ligands determined the properties of the borates by altering the geometry and were consistently bound to the metal center by chelation. The synthesized compounds were L?B(OC6H4)3CH, L?B(OC6H4)3SiMe, and its derivatives (L=THF or pyridine as an external ligand). Theoretical calculations suggested that the cage‐shaped borates had a large dihedral angle (Cipso‐O‐B‐O) compared with open‐shaped borates. The geometric effect due to the dihedral angle means that compared with open‐shaped, the cage‐shaped borates have a greater Lewis acidity. The introduction of electron‐withdrawing groups on the aryl moieties in the cage‐shaped framework increased the Lewis acidity. Substitution of a bridgehead Si for a bridgehead C decreased the Lewis acidity of the boron complexes because the large silicon atom reduces the dihedral angle of Cipso‐O‐B‐O. The ligand‐exchange rates of the para‐fluoro‐substituted compound B(OC6H3F)3CH and the ortho‐phenyl‐substituted compound B(OC6H3Ph)3CH were less than that of the unsubstituted borate B(OC6H4)3CH. The ligand‐exchange rate of B(OC6H4)3SiMe was much faster than that of B(OC6H4)3CH. A hetero Diels–Alder reaction and Mukaiyama‐type aldol reactions were more effectively catalyzed by cage‐shaped borates than by the open‐shaped borate B(OPh)3 or by the strong Lewis acid BF3?OEt2. The cage‐shaped borates with the bulky substituents at the ortho‐positions selectively catalyzed the reaction with less sterically hindered substrates, while the unsubstituted borate showed no selectivity. 相似文献
54.
Keiichiro Ishikawa Nobuyasu Hanari Yoshitaka Shimizu Toshihide Ihara Akira Nomura Masahiko Numata Takashi Yarita Kenji Kato Koichi Chiba 《Accreditation and quality assurance》2011,16(6):311-322
Purity assay of high-purity materials (HPMs) of phthalic acid esters (PAEs) was carried out by means of a mass balance method.
In this method, chromatographic methods such as gas chromatography-flame ionization detector (GC-FID) and/or high-performance
liquid chromatography (HPLC) in combination with other methods such as Karl-Fischer (KF) titration and vacuum evaporation
(VE) were applied. The sum of the impurities estimated by these methods allowed the estimation of the purity of the main component
by difference. Seven PAEs with varying side chain structures and levels of impurities were analysed on a systematic way in
which impurities were classified into several groups in terms of their abundance, availability of qualitative information
and availability of authentic compounds, etc. The absolute quantity of each impurity was determined by GC-FID and/or HPLC
based on the calibration made by the authentic compounds of impurities whenever available. The purities in mass fraction of
these PAEs were certified at the National Metrology Institute of Japan (NMIJ), and the PAEs were registered as primary reference
materials playing an essential role in linking the metrological traceability of the Japan Calibration Service System (JCSS)
to the International System of Units (SI). 相似文献
55.
Ultraviolet irradiation, which is environment friendly and without any chemical pollution, was used to functionalize high‐density polyethylene (HDPE) and to improve the interfacial interaction of its composites with sericite in this study. The oxygen‐containing groups of C?O, C‐O, and C(?O)O were quickly introduced onto molecular chains of HDPE by ultraviolet irradiation in ozone atmosphere and the contents of the introduced oxygen‐containing groups increased with increasing the modification time. It is important to note that the irradiation time greatly decreased compared to that in air or oxygen atmosphere. After modification, the molecular weight of the irradiated HDPE decreased and its distribution became wider. The irradiated HDPE in ozone was not crosslinked, which is an advantage over the same reaction in air or oxygen atmosphere. With increasing the irradiation time, the melting temperature of the irradiated HDPE lightly decreased, while its crystallinity, hydrophilicity, and fluidity increased. The composites of HDPE/sericite were prepared. The results showed that the dispersion of sericite in the matrix and the interfacial interaction of sericite with the matrix were markedly improved for the irradiated HDPE/sericite composites. As a result, the irradiated HDPE/sericite composites showed significantly increased tensile yield strength and notched impact strength. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
56.
Aiming to find rigorous understanding and novel features for their potential applications, the physico-geometrical kinetics of the thermal decomposition of sodium hydrogencarbonate (SHC) was investigated by focusing on the phenomenological events taking place on a single crystalline particle during the course of the reaction. The overall kinetics evaluated by systematic measurements of the kinetic rate data by thermogravimetry under carefully controlled conditions were interpreted in association with the morphological studies on the precursory reaction, mechanism of surface reaction, structure of the surface product layer, diffusion path of evolved gases, crystal growth of the solid product, and so on. The precursory reaction was identified as the decomposition of impurity, taking place at the boundary between the surface of the SHC crystal and the adhesive small SHC particles deposited on the surface. In flowing dry N(2), the thermal decomposition of SHC proceeds by two-dimensional shrinkage of the reaction interface controlled by chemical reaction with the apparent activation energy of about 100 kJ mol(-1), after rapid completion of the surface reaction and formation of porous surface product layer. Atmospheric CO(2) and water vapor influence differently on the overall kinetics of the thermal decomposition of SHC. Added gas phase of CO(2) slightly inhibits the overall rate because of the increasing contribution of the surface reaction. Under higher water vapor pressure, the physico-geometrical mechanism of the surface reaction changes drastically, indicating the preliminary reformation of reactant surface and the formation of needle crystals of solid product on the surface. The mechanistic change and extended contribution of the surface reaction result in the deceleration of the surface reaction and acceleration of the established reaction. 相似文献
57.
Copper-catalyzed benzylic C-H oxygenation under an oxygen atmosphere was developed starting from carbonitriles and Grignard reagents via N-H imine intermediates. The present process is characterized by the following two-step sequence in a one-pot manner: (1) addition of Grignard reagents to carbonitriles to form N-H imines and (2) benzylic C-H oxygenation (C═O bond formation) triggered by 1,5-hydrogen atom transfer with transient iminyl copper species. 相似文献
58.
Ohno O Chiba T Todoroki S Yoshimura H Maru N Maekawa K Imagawa H Yamada K Wakamiya A Suenaga K Uemura D 《Chemical communications (Cambridge, England)》2011,47(46):12453-12455
Novel sesquiterpene alkaloids, halichonines A (1), B (2), and C (3), were identified from the marine sponge Halichondria okadai Kadota. By spectroscopic analyses and synthesis, their structures were revealed to include a 6,6-bicyclic ring system and two prenylated amine moieties. In addition, 2 induced apoptosis in HL60 human leukemia cells. 相似文献
59.
Tsuyoshi Mayama Masafumi NodaRyoichi Chiba Mitsutoshi Kuroda 《International Journal of Plasticity》2011,27(12):1916-1935
The texture development mechanism during the extrusion of magnesium alloy is investigated by experimental observation and numerical analysis. First, we perform a finite element analysis of a full extrusion process using a phenomenological constitutive equation, and it is confirmed that the loading condition of the extrusion process near the central axis of the billet is approximated by an equi-biaxial compression mode. Then, the equi-biaxial compression problem is adopted as a simplified boundary value problem to be solved using a crystal plasticity model to clarify the detailed texture development mechanism during the extrusion process. The crystal plasticity analysis of equi-biaxial compression successfully reproduces the texture development from an initial random texture to the final experimentally observed texture. The effects of the deformation modes (i.e. slip and twinning systems) implemented in the calculation and the reference stress ratio of basal to nonbasal slip systems on texture development are studied in detail. Finally, the mechanism of texture development during the extrusion process is discussed in terms of the lattice rotation caused by the activated slip systems. 相似文献
60.
Unexpected vibrations on a cylindrical filter made of nonwoven fabrics were clarified experimentally. Two types of filter with length L=1.8 m and 3.7 m, both 45 cm in diameter and 1.08 mm in thickness, were used. This is a new type of aeroelastic vibration phenomenon because the filter is a closed cylindrical vessel. In addition, the flow velocity of inner air was very slow and inner air flowed out slowly from the filter surface. The velocity distribution of air flow from a fan duct as well as the frequency and amplitude of the filter vibration were measured for two types of filter. By setting up a roll core panel at the outlet of the fan duct, we could rectify the outflow and suppressed the vibration of the shorter filter with L=1.8 m. However, this method was not adequate for the longer filter with L=3.7 m, and we could suppress the vibration by shielding the inner surface of the filter at the top region. 相似文献