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991.
Water-soluble polysaccharides have been isolated from two species ofEremurus — E. lactiflorus andE. luteus — with yields of 13.5% and 20.5%, respectively. They contained mainly glucose and mannose in ratios of 1:5 and 1:3.1. The polysaccharides ofE. lactiflorus were separated from a column of DEAE-cellulose. The yield of neutral fraction was 10.3%. Gel filtration of the polysaccharides on Sephadex G-200 showed their polydispersity. Homogeneous fractions were obtained by fractional precipitation with ethanol. They have been characterized with respect to monosaccharide composition, molecular weight, and IR spectra. 相似文献
992.
A procedure is described for the polarographic determination of tellurium in lead alloys, without resorting to prior separative techniques. Interference by Cu, Cd, Tl, As, and Sb is discussed. 相似文献
993.
Ming Z. Gao 《Tetrahedron letters》2004,45(29):5649-5652
The novel structures of sulfur-containing chiral bis(oxazoline) compounds which have been synthesized have been determined by X-ray crystal diffraction analyses. A high enantioselectivity (ee >99%) in the asymmetric cyclopropanation of diphenylethene with diazoester using the bis(oxazoline)-Ru(II) catalyst was obtained. 相似文献
994.
The process of wastewater treatment to remove ammonium ions by precipitation in the form of ammonium magnesium phosphate was studied. The fundamental aspects of the chemical precipitation process were examined. The effect of various factors on the efficiency of wastewater treatment was experimentally analyzed. 相似文献
995.
Qin XZ 《Journal of mass spectrometry : JMS》2001,36(8):911-917
Compound 1 (1-(3-chlorophenyl)-4-[1-(4-cyanobenzyl)imidazolylmethyl]-2-piperazinone hydrochloride) is a farnesyl transferase inhibitor intended for treatment of cancer. A detailed analysis of the electrospray ionization mass spectrometry and tandem mass spectrometry data of protonated 1 shows that in the gas phase, upon collision-induced dissociation, this ion undergoes complicated rearrangement and fragmentation. These processes include a novel two-step rearrangement. The first step involves a gas-phase intramolecular S(N)2 reaction that forms an intermediate. The second step consists of three competitive rearrangement/fragmentation pathways of the intermediate, giving rise to protonated 2, protonated methylene-imidazole, and a distonic methylimidazole radical cation. Deuterated 1 was studied under the same experimental conditions, and the results strongly support the proposed two-step rearrangement process. It is noted that the unique structure of 1, especially the imidazole ring of 1, plays a critical role in the rearrangement of protonated 1. 相似文献
996.
The heat transfer mechanisms in inorganic hollow micro-spheres filled polymer composites are analyzed in the present paper. This heat transfer includes mainly three mechanisms: (1) thermal conduction between solid and gas; (2) thermal radiation between the hollow micro-sphere surfaces; and (3) natural thermal convection of the gas in the micro-hollow spheres. A theoretical model of heat transfer in polymer/inorganic hollow micro-sphere composites is established based on the law of minimal thermal resistance and the equal law of the specific equivalent thermal conductivity, and a corresponding equation of effective thermal conductivity is derived. The effective thermal conductivity (keff) of hollow glass bead-filled polypropylene composites is estimated by using this equation, and is compared with the numerical simulations by means of a finite element method. The results show that the variation of the theoretical estimations of keff are similar to the numerical simulations at lower filler volume fraction (φf20%). Moreover, keff decreases linearly with increasing φf, and reduces somewhat with increase of filler size. 相似文献
997.
Z. Mikulová P. Čuba J. Balabánová T. Rojka F. Kovanda K. Jirátová 《Chemical Papers》2007,61(2):103-109
The effect of hydrothermal treatment on properties (crystallinity, porous structure, reducibility, acidity, basicity, and
catalytic activity and selectivity in toluene and ethanol total oxidation) of Ni—Al layered double hydroxide precursors and
related mixed oxides was examined. The hydrothermal treatment increased considerably both the content of crystalline phase
and LDH crystallite size. On the other hand, only a slight effect of the precursor hydrothermal treatment on crystallinity
of the related Ni—Al mixed oxides obtained by calcination at 450°C was observed. The reducibility of NiO particles appeared
to be hindered considerably compared to the reducibility of pure NiO. Catalytic activity of the Ni—Al mixed oxides prepared
from the precursors hydrothermally treated for a short time (4 h) was the highest. The highest amount of acetaldehyde formed
during the total oxidation of ethanol, i.e. the worst selectivity was found for the calcined Ni—Al LDH without hydrothermal treatment.
Presented at the 33rd International Conference of the Slovak Society of Chemical Engineering, Tatranské Matliare, 22–26 May
2006. 相似文献
998.
The effect of the size and branching of alkyl substituents R1 and R2 on the formation of all possible stereoisomers of bis(β-acylvinyl)amines, [R1COCR2CH]2NH, has been investigated. IR and NMR data show that steric requirements of these substituents and resonance stabilization of the s-trans system are the main factors determining the position of the dynamic equilibrium. 相似文献
999.
Feng DH Xu ZZ Feng XL Jia TQ Li XX Liu JS 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2005,61(4):575-578
Incoherent subharmonic light scattering in isotropic media is a new kind of nonlinear light scattering, which involves single input photon and multiple output photons of equal frequency. We investigate theoretically the dependence of the subharmonic scattering intensity on the hyperpolarizability of molecules and the incident intensity using nonlinear optics theory similar to that used for Hyper-Rayleigh scattering and degenerate optical parametric oscillators. It is derived that the subharmonic scattering intensities grow exponentially or superexponentially with the hyperpolarizability of molecules and the incident intensity. 相似文献
1000.