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221.
A kinetic–catalytic spectrophotometric method is proposed for the successive determination of nanogram levels of copper and iron, which is based on their catalytic effects on the oxidative coupling of p-anisidine with N,N-dimethylaniline (DMA) to form a colored compound (λmax=740 nm) in the presence of hydrogen peroxide at pH 3.2. 2,9-Dimethyl-1,10-phenanthroline (neocuproine) acted as an activator for the copper catalysis, and 1,10-phenanthroline (phen) acted as an activator for the iron catalysis. The selectivity was improved in the presence of diphosphate as a masking agent. The determinable ranges were 0.16–10 ppb for copper and 1–100 ppb for iron, respectively. The relative standard deviations of copper and iron were 1.1 and 0.97% for five determinations of 10 ppb copper and 40 ppb iron. The method was successfully applied to the analyses of copper and iron in tap, well, river and pond waters. 相似文献
222.
Tadao Uyehara Yasuhiro Kabasawa Tadahiro Kato Toshiaki Furuta 《Tetrahedron letters》1985,26(19):2343-2346
The total synthesis of (±)-pinguisone and (±)-deoxopinguisone, the unusual [5–6], fused-ring sesquiterpenes, was accomplished by the photochemical transformation of the bicyclo [3.2.2]non-6-en-2-one into the bicyclo [4.3.0]non-4-en-7-one. 相似文献
223.
224.
We succeeded in a first total synthesis of flavocommelin (1), a component of the blue supramolecular pigment, commelinin (2), from Commelina communis, by direct 6-C-glycosylation of the flavan 4 using perbenzylglucosyl fluoride 8 in the presence of MS 5 angstroms in CH2Cl2 and a catalytic amount of BF3 x Et2O. After 6-C-glycosylation of 4, oxidation with CAN to flavanone 18 and subsequent 4'-O-glycosylation, promoted with a combination of BF3 x Et2O and DTBMP, afforded diglucosylflavanone 20. DDQ oxidation of 20 and deprotection successively gave 1. 相似文献
225.
2-(5-Bromo-2-pyridylazo)-5-(N-propyl-N-sulfopropylamino)aniline rapidly forms a water-soluble complex with palladium in an acetate-buffered medium at pH 3.2.The molar absorptivity of the complex is 9.84×104l mol?1 at 612 nm. The calibration graph is linear over the range of 10–100 μg l?1 palladium; the detection limit is 2 μg l?1 and the relative standard deviation is 0.6% for 100 μg l?1 palladium. The sample throughput is 50 h?1. Divalent transition metals (Fe, Ni, Co) do not interfere at levels from 2 to 10 mg l?1. Interference from copper is prevented by adding 10?3 M EDTA solution to the carrier stream. Palladium in solutions of catalysts and dental alloys can be determined selectively, sensitively and rapidly. 相似文献
226.
The effects of water content on the growth rate and the final particle size of AgCl nanoparticles in a reversed micelle (RM) system of polyoxyethylene (6) nonylphenyl ether (NP-6)/water/cyclohexane were investigated using a double-jet technique, in which RM solutions of AgNO(3) and KCl were added concurrently to a RM solution containing the excess concentration of chloride ion. As a result, the particle growth rate and the final particle size at a constant Rw ( identical with[water]/[surfactant]) below 5 were found to be in excellent agreement with our theoretical prediction based on a dynamic Ostwald ripening mechanism governed by the overall solubility of the solid and the diffusivity of the reversed micelles, whereas the final particle size was far beyond the size of the water pool of a reversed micelle. Thus, the dramatic reduction of the particle size in the RM system can be explained by the drastic reduction of the overall solubility of the solid and the small diffusivity of the bulky reversed micelles as a carrier of silver ion, and not by the size of the water pool of a reversed micelle as conventionally explained. Some additional contribution of a coagulation process was also suggested in a high Rw range above 5. Significant coagulation of AgCl particles was observed in a RM system with AOT in place of NP-6 even under the standard conditions for the NP-6 system. 相似文献
227.
Uniform anatase-type TiO(2) nanoparticles of different shapes have been formed by phase transformation of a Ti(OH)(4) gel matrix in the presence of shape controllers. For example, triethanolamine (TEOA) was found to change the morphology of TiO(2) particles from cuboidal to ellipsoidal at pH above 11. The shape control can be explained in terms of the specific adsorption of TEOA onto the crystal planes parallel to the c-axis of the tetragonal system in the alkaline range, as supported by the observation of preferential adsorption of TEOA onto the crystal planes parallel to the c-axis at pH 11.5 and by the pH dependence of the adsorption onto ellipsoidal particles. Diethylenetriamine (DETA) also modified the particle shape to ellipsoidal above pH 9.5 and the aspect ratio was much higher than with TEOA. The mechanism of the shape control could be explained in the same way as with TEOA, since analogous specific adsorption was observed with DETA as well. Similar shape control to yield ellipsoidal particles of a high aspect ratio was also achieved with other primary amines, such as ethylenediamine (ED), trimethylenediamine (TMD), and triethylenetetramine (TETA). However, secondary amines, such as diethylamine, and tertiary amines, such as trimethylamine and triethylamine, acted as a complexing agent of Ti(IV) ions to promote the growth of ellipsoidal particles of a low aspect ratio, rather than a shape controller to produce ellipsoids of a high aspect ratio. Sodium oleate and sodium stearate were found to modify the particle shape from round-cornered cubes to sharp-edged cubes. The mechanism was explained in terms of the reduction of the specific surface energies of the [001] and [100] planes of the tetragonal crystal system by the preferential adsorption of oleate or stearate ion onto these planes, based on the adsorption experiment using ellipsoidal and cubic particles. 相似文献
228.
Toshio Goto Tadao Kondo Hirotoshi Tamura Hiroyuki Imagawa Aya Iino Kosaku Takeda 《Tetrahedron letters》1982,23(36):3695-3698
Structure of gentiodelphin is determined to be 5, 3′-d8-O-(6-O--caffeoylβ-D-glucosyl)-3-O-(β-D-glucosyl)delphinidin. The anthocyanin is stable in dilute neutral aqueous solution. This stabilization may be caused from intramoleculaur hydrophobic interactions among the aromatic nuclei; the anthocyanidin being sandwiched win between two caffeic acids. 相似文献
229.
Blue sepal-color of Hydrangea macrophylla might be due to a supramolecular metal-complex pigment consisting of delphinidin 3-glucoside (1), co-pigments (5-O-caffeoylquinic acid (2), and/or 5-O-p-coumaroylquinic acid (3)) and Al3+ in an aqueous solution around pH 4.0. To clarify the mechanism of blue sepal-color development of hydrangea, we tried to reproduce the blue color in vitro by mixing 1 with designed synthetic co-pigments in the presence of Al3+ at pH 4.0. We at first succeeded in clarifying the essential functional structure in the co-pigment that could form the stable blue solution. Here, we present the structure of the blue pigment caused by an Al-complex coordinating of 1 at ortho-dihydroxyl groups of the B-ring, 1-hydroxy, 1-carboxylic acid, and the carbonyl residue in the ester at 5-position of 2 and/or 3. The hydrophobic interaction between the aromatic acyl residue at 5-position and the nucleus of 1 may also contribute to stabilize the complex. 相似文献
230.
Structure of cinerarin is determined to be 3-0-(6-0-malonyl-β-D-glucopyranosyl)-7-0-(6-0-(4-0-(6-0-caffeyl-β-D-glucopyranosyl)caffeyl)-β-D-glucopyranosyl)-3′-0-(6-0-caffeyl-β-D-glucopyranosyl)delphinidin. 相似文献