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排序方式: 共有262条查询结果,搜索用时 15 毫秒
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Summary Traces of molybdenum in sea water have been preconcentrated by anion-exchange from acidified samples in the presence of sodium azide. Molybdenum adsorbs strongly on a column of Bio-Rad AG 1 (Cl–) and can be stripped easily by elution with 2 mol/l NH4Cl — 2 mol/l NH4OH solution. Molybdenum in the effluent is determined by graphite furnace atomic absorption spectrometry. The combined method allows to determine traces of molybdenum in sea water as well as non-saline water on a 100 ml sample basis. The method gives a relative standard deviation of better than 8% at a molybdenum level of 10 g 1–1 of sea water.
Bestimmung von Molybdänspuren in Meereswasser mit Hilfe einer Kombination von Anionenaustausch und elektrothermischer Atomabsorptionsspektrometrie相似文献
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A number of nitrato complexes of metals have been found to be adsorbed on DEAE-cellulose from mixed acetic acid-nitric acid media, although none can be adsorbed from aqueous nitric acid solutions. The distribution coefficients of Sc, Mo, La, Sm, W, Re, Bi, Th and U are given as functions of acetic acid and nitric acid concentrations (sometimes in the presence of hydrogen peroxide to prevent hydrolytic precipitation). For 25 other metals column adsorption behaviour is described for a 90% acetic acid-10% 7.6M nitric acid mixture. Favourable differences in the distribution coefficients allow useful separations such as FeMoW and USmMoBiTh, to be achieved. 相似文献
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Summary The adsorption behaviour of 48 metal ions on DEAE-cellulose layers has been investigated in aqueous hydrobromic and hydriodic acid media. RF values are given as a function of the hydrobromic and hydriodic acid concentration over the ranges 0.01–6 mol dm–3 and 0.01–3 mol dm–3, respectively, and are compared with those obtained with Avicel SF. RF spectra are comparatively simple in both media, reflecting the strong affinity of the bromide and iodide ions to the DEAE-cellulose phase. Pd, Pt, Re, Au and Hg are distributed chromatographically in either system, while most other metal ions exhibit rather extreme RF values of near unity or zero. Therefore, the selectivity of the systems is particularly high for Pd, Pt, Re, Au and Hg, providing the possibility of their excellent selective separations. 相似文献
6.
A new-type of sol-gel/organic hybrid composite material using gelatin or chitosan with tetramethoxysilane was developed for the bovine serum albumin (BSA)-encapsulated monolithic column for capillary electrochromatography (CEC). The composite monolith was used to immobilize BSA in a fused-silica capillary. The addition of gelatin and chitosan to the alkoxysilane enabled the enantioseparation of Trp. A very small amount of these polymers were effective for the enantioseparation. Especially, the monolithic column prepared from chitosan with tetramethoxysilane showed a high enantioselectivity for Trp enantiomers and the value (alpha' = t2/t1, t1: fast eluted enantiomer, t2: second eluted enantiomer) reached 1.15 on CEC mode. Furthermore, the composite materials exhibited a higher stability compared to the silica sol-gel column. These results showed that the sol-gel/organic hybrid composite was useful as a monolithic matrix for the BSA-encapsulated column for CEC. 相似文献
7.
Ohno H Takeoka Y Kadoh Y Miyamura K Tanaka T 《The Journal of organic chemistry》2004,69(13):4541-4544
Two novel palladium(0)-catalyzed cyclizations of allenenes are described. Treatment of allenenes such as N-(1-alkyl-2,3-butadienyl)-N-allylsulfonamide with an aryl halide and K(2)CO(3) in the presence of a catalytic amount of Pd(PPh(3))(4) in dioxane affords 2,3-cis-pyrrolidines in a stereoselective manner. In sharp contrast, cyclization of the same allenenes using catalytic Pd(2)(dba)(3) x CHCl(3) in the presence of allyl methyl carbonate in CH(3)CN leads to stereoselective formation of a 3-azabicyclo[3.1.0]hexane framework in moderate yields. 相似文献
8.
Kadota I Ohno A Matsuda K Yamamoto Y 《Journal of the American Chemical Society》2002,124(14):3562-3566
The Lewis acid mediated reaction of alpha-acetoxy ethers 15-22 gave the corresponding cyclized products 23, 25, 27, 29, 31, 32, 34, and 36 in good yields with high stereoselectivities. Those cyclized products were subjected to ring-closing metathesis to afford the polycyclic ethers 38-42, 44, and 45 in good yields. The usefulness of the present methodology was demonstrated by the convergent synthesis of the CDEF ring system of brevetoxin B (1) and the CDEFG ring system of gambierol (2). 相似文献
9.
Sansei Nishibe Kumiko Mitsui-Saitoh Junichi Sakai Takahiko Fujikawa 《Molecules (Basel, Switzerland)》2021,26(8)
Forsythia fruit (Forsythia suspensa Vahl (Oleaceae)) is a common component of Kampo medicines for treating the common cold, influenza, and allergies. The main polyphenolic compounds in the leaves of F. suspensa are pinoresinol β-d-glucoside, phillyrin and forsythiaside, and their levels are higher in the leaves of the plant than in the fruit. It is known that polyphenolic compounds stimulate lipid catabolism in the liver and suppress dyslipidemia, thereby attenuating diet-induced obesity and polyphenolic anti-oxidants might attenuate obesity in animals consuming high-fat diets. Recently, phillyrin was reported as a novel cyclic AMP phosphodiesterase 4 (PDE4) inhibitor derived from forsythia fruit. It was expected that the leaves of F. suspensa might display anti-obesity effects and serve as a health food material. In this review, we summarized our studies on the biological effects of forsythia leaves containing phillyrin and other polyphenolic compounds, particularly against obesity, atopic dermatitis, and influenza A virus infection, and its potential as a phytoestrogen. 相似文献
10.
Asao N Takahashi K Lee S Kasahara T Yamamoto Y 《Journal of the American Chemical Society》2002,124(43):12650-12651
The reaction of o-alkynylbenzaldehydes 1 and alkynes 2 in the presence of a catalytic amount of AuCl3 in (CH2Cl)2 at 80 degrees C gave naphthyl ketone products in high yields. The AuCl3-catalyzed formal [4 + 2] benzannulation proceeds most probably through the coordination of the triple bond of 1 to AuCl3, the formation of benzo[c]pyrylium auric ate complex via the nucleophilic addition of the carbonyl oxygen atom, the Diels-Alder addition of alkynes 2 to the auric ate complex, and subsequent bond rearrangement. Similarly, the AuCl3-catalyzed reactions of o-alkynylacetophenone and o-alkynylbenzophenone with phenylacetylene afforded the corresponding naphthyl ketone products in good yields. 相似文献