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991.
Summary. Single crystals of sodium dithiophosphate undecahydrate (Na3PO2S2 · 11H2O) and sodium trithiophosphate undecahydrate (Na3POS3 · 11H2O) were grown from aqueous solution. The crystal structures of Na3PO2S2 · 11H2O (P212121; a = 1248.1(1), b = 945.2(1), c = 1383.1(1) pm; R
1 = 0.0202, wR
2 = 0.0502) and Na3POS3 · 11H2O (Pna21; a = 1262.0(2), b = 947.6(2), c = 1431.5(2) pm; R
1 = 0.0720, wR
2 = 0.1371) are related to each other in a sense that all constituting units are arranged in similar positions and with similar
orientations. The geometries of the anions were determined with high accuracy; thus, the structural parameters of the POS3−
3 anion were measured for the first time.
Received September 25, 2001. Accepted January 21, 2002 相似文献
992.
This article describes a dream of Little R visiting the 'Chiral Molecule Museum'. It introduces the structure of chiral molecules, the experiment to demonstrate the existence of chiral molecules-experiments on the separation of optical isomers of sodium ammonium tartrate by Pasteur, the two enantiomers of limonene; chiral drug thalidomide, and asymmetric catalysis. 相似文献
993.
Effect of intercalated reactive mica on water absorbency for poly(sodium acrylate) composite superabsorbents 总被引:2,自引:0,他引:2
A series of superabsorbents based on sodium acrylate (NaA), mica (MI), and N,N′-methylene-bis-acrylamide (NMBA) were prepared by inverse suspension polymerization. The influences of the type and content of mica such as pure K+-MI and intercalated-MI (IMI) in the composite gels on the water absorbency and the initial absorption rate in deionized water and salt solutions were investigated. Results showed that the water absorbency and initial absorption rate gradually decrease with increasing amounts of pure K+-MI and intercalated-MI. In addition, the water absorbency and initial absorption rate for the gels prepared by intercalated-MI were lower than those prepared by pure K+-MI. 相似文献
994.
995.
测定了 4个分子量和分子量分布不同、M G不同的海藻酸钠试样在不同浓度下的恒温 (2 5℃ )动态粘弹谱 ,发现 4个试样随溶液浓度升高都会发生溶胶 凝胶 (Sol gel)转变 .实验结果表明 ,该转变符合Winter和Chambon的凝胶化点临界状态的松弛模量G(t)方程 ,由tanδ不依赖于ω的判据求出了海藻酸钠水溶液随浓度变化发生Sol gel转变、出现物理凝胶化的凝胶化点溶液浓度cgel和临界指数n .cgel=7 6wt%~ 8 0wt% ,基本与分子量无关 ;分子量较高的 3个试样的n =0 32~ 0 38,而分子量低的试样的n =0 6 1.该结果表明 ,物理凝胶化主要是由大分子重复单元间的相互作用决定 ,分子链越长则凝胶化点的交联结构越完善 相似文献
996.
997.
Na5Br(OH)4: Synthesis and Structure of a Compound in the System NaOH/NaBr The pseudobinary system NaOH/NaBr is investigated by X-ray methods. The structure of the compound Na5Br(OH)4 was solved by single crystal data: Na5Br(OH)4: Pnma, Z = 8, a = 11.846(2) Å, b = 18.782(4) Å, c = 6.431(1) Å, Z(Fo) = 1 202 with (Fo)2 ≥ 3σ(Fo)2, Z(parameter) = 100, R/Rw = 0.030/0.035 The compound crystallizes in a new type of structure. Pairs of octahedra around O by 5 Na and 1 H to [Na5(OH)]2 are orientated in such a way to one another that two ions OH? form a parallelogram hinting to unusual bent hydrogen bridge bonding. 相似文献
998.
Summary A method for simultaneous determination of Cr(III) and Cr(VI), using sodium diethyldithiocarbamate as chelating agent is given. At room temperature and pH 5.8 sodium diethyldithiocarbamate reacts with both Cr(III) and Cr(VI). Examination of this reaction by reversed phase high-performance liquid chromatography, makes it possible to correct for the interference between Cr(III) and Cr(VI) when determining the amount of Cr(III) present in the solution. 相似文献
999.
1000.
This paper presents an automatic spectrofluorimetric method (flow injection analysis spectrofluorimetry) for detecting hydroxyl radicals. Based on H2O2 catalyzed by Co2+ yielding HO, the method utilized sodium terephthalate to trap hydroxyl radicals and obtained sodium 2-hydroxyterephthalate by aromatic hydroxylation, which resulted in an increase in the fluorescence intensity. The relative fluorescence intensity was proportional to the concentration of hydroxyl radicals. Hydroxyl radicals could be determined indirectly, based on the increase of fluorescence. It was a simple, rapid, precise, sensitive and automatic technique for the determination of HO. The relative standard deviation of 11 determinations was 0.57%. The method can be used to sieve antioxidant medicines and will have theoretical and practical guidance on the mechanism of hydroxyl radicals-damaging biology. 相似文献