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171.
A new simple, rapid and sensitive spectrophotometric flow injection method for the determination of trace iodide is described
based on an ion associate of iodate (IO3
–) with 2- (3,5-dibromo-2-pyridylazo)-5-diethylamino-phenol (3,5-Br2-PADAP) and thiocyanate (SCN–). In a strongly acidic medium, this unstable violet product was formed with an absorption maximum at 605 nm. Flow injection
is an ideal method to reproducibly monitor the transient signal. Various parameters were optimized using the Super Modified
Controlled Weighted Centroid Simplex Method (SMCWC). Under the optimum experimental conditions, iodide could be determined
in the range of 1.00 × 10–6 and 2.4 × 10–5 mol l–1. The correlation coefficient of the calibration curve is 0.9991. With a sampling frequency of 80 h–1, the detection limit for iodide is 5.0 × 10–7 mol l–1. The proposed method has been applied to the determination of trace iodide after oxidizing I– in table salt or laver to IO3
–. In addition, the mechanisms of the ion association reaction was studied.
Received: 15 August 1996 / Revised: 10 October 1996 / Accepted: 16 October 1996 相似文献
172.
The chemical fixation of CO2 with mono-substituted terminal epoxides or cyclohexene oxide to form cyclic carbonates under the ZnCl2/[BMIm]Br catalyst system without using additional organic solvents was achieved in excellent selectivity (>98%) and TOF (5410 h−1) and the catalyst could be used six times almost without losing its catalytic activity and selectivity. Besides, the pure cis-cyclic carbonate of cyclohexene oxide was obtained in this catalyst system. 相似文献
173.
在进行有机氯化物分子内非键合相互作用的热化学研究中, 为了排除分子间的相互作用, 需要准确的标准蒸发焓或升华焓, 以便把凝聚态的标准生成焓转变为气态的数据。文献中多氯代烷烃的蒸发焓数据不多, 其中由直接量热法得到的准确数据更少, 因此我们测量了一些多氯代烷烃的标准蒸发焓, 并对其规律作了一些探讨。 相似文献
174.
The three new lignanoids 1 – 3 and the five new phyllocladane diterpenoids 7 – 11 were isolated from the leaves of Callicarpa furfuraceae, together with two known lignanoids, lariciresinol ( 4 ) and (+)‐sesamin ( 5 ), and five known diterpenoids, 17‐norphyllocladane‐3,16‐dion ( 6 ), calliterpenone ( 12 ), calliterpenone 17‐acetate ( 13 ), (3β,16α)‐phyllocladane‐3,16,17‐triol ( 14 ), and (3β,16α)‐phyllocladane‐3,16,17‐triol 17‐acetate ( 15 ). Their structures were established by spectral‐data interpretation. 相似文献
175.
A novel compound, [Co(phen)3][V10O26]·H2O, was hydrothermally synthesized and characterized by single-crystal X-ray diffraction. This compound crystallizes in the orthorhombic space group Ccca with a=13.447(3), b=29.936(6), c=23.252(5) Å, V=9360(3) Å3, Z=8 and R=0.0285. Data were collected on a Rigaku R-AXIS RAPID IP diffractometer at 293 K in the range of 1.36<θ<24.99°. The structure of the compound consists of vanadium oxide layers, which are built up from the infinite VO4 chains by corners and edges sharing. The [Co(phen)3]2+ complexes occupy the interlayer space and contact each other via π−π stacking interactions of the phen groups to form infinite one-dimensional chains. 相似文献
176.
Starting from readily available carbohydrates the synthesis of 8-epi-(+)-boronolide 19 and (+)-boronolide was achieved with diastereoselective propargylation of alpha-oxygenated aldehyde as a key step. 相似文献
177.
Cheng Chu Zeng Li Ming Hu Jia Zeng Ru Gang Zhong College of Life Science & Bioengineering Beijing University of Technology Beijing China 《中国化学快报》2007,18(2):130-132
The anodic oxidation of caffeic acid in the presence of acetylacetone or methyl acetoacetate in aqueous solution has been studied by cyclic voltammetry and controlled-potential electrolysis techniques. The result showed that caffeic acid was oxidized to the corresponding o-benzoquinone, which underwent further Michael-addition with acetylacetone or methyl acetoacetate to produce caffeic acid derivative 3,4-dihydroxy-6-(1-acetylacetone)-yl cinnamic acid 4a or 3,4-dihydroxy-6-(1-acetyl-methylacetate)-yl cinnamic acid 4b. 相似文献
178.
The base-catalyzed addition of thiamin to benzaldehyde produces 2-(1-hydroxybenzyl)thiamin (HBnT), but in neutral solution HBnT undergoes base-catalyzed irreversible fragmentation into pyrimidine and thiazole derivatives. The fragmentation (rather than elimination) occurs in proportion to the extent that N1' is protonated or alkylated. Generating the conjugate base of HBnT by decarboxylation surprisingly leads to fragmentation independent of the state of N1'. Therefore, a cationic state at N1' specifically promotes removal of the C2alpha proton rather than the fragmentation process itself. It is suggested that benzoylformate decarboxylase, which generates a similar intermediate, exerts stereoelectronic control of the conformation of the carbanion, blocking fragmentation and facilitating protonation. 相似文献
179.
In this study, we developed an analytical method for the enantioseparation of ofloxacin, using capillary electrophoresis with fluorescence detection. The optimum background electrolyte was obtained to be 60 mM hydroxylpropyl‐β‐cyclodextrin (HP‐β‐CD) in 50 mM phosphate buffer at pH 2.30. Under these conditions, the (+) and (‐) ofloxacin were completely separated, with the detection limit of 10 nM when the sample was prepared in deionized water. The linear ranges of levofloxacin in deionized water and untreated urine were 10?7 to 5 × 10?3 M with R2 = 0.9989 and 5 × 10?6to 5 × 10?3 M with R2 = 0.9943, respectively. We also applied this method to investigate the purity of a commercial drug. The results revealed that the ratio between (+)‐ofloxacin and (‐)‐ofloxacin (levofloxacin) was 99.9:0.1, and there is about 93 mg levofloxacin per tablet (200 mg). The concentration of levofloxacin in patient's urine was founded to be 7.9 × 10?4M, and the ratio between the two optical isomers was 99.3:0.7. 相似文献
180.
Shen J Ye Y Hu J Shen H Le Z 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2001,57(3):551-559
Copper(II), zinc(II), cobalt(II) and cobalt(III) complexes of N-D-glucosamine beta-naphthaldehyde (C17H19O6N, NG) and glycine were synthesized. The four novel metal complexes, Cu(II)C19H28O11N2(CuGNG), Zn(II)C19H24O9N2 (ZnGNG), Co(II)C19H28O11N2(Co(II)GNG) and Co(III)C21H29O12N2(Co(III)GNG) were characterized by means of infrared (IR), electronic absorption spectroscopy and NMR etc. The surface-enhanced Raman spectra of the four complexes and their interaction with DNA were studied. By comparison of the surface-enhanced Raman spectra (SERS), the information of the four complexes' SER active sites and adsorption orientation were obtained. Combined with fluorescence spectra of Ethidium bromide (EthBr) DNA system, we concluded that none of the four complexes intercalate into DNA and that the presence of the glycine ligand lowered the anticancer activity of NG series complexes. 相似文献