The bromination of 6,7,8,9-tetrahydro-5H-5,9-ethenobenzo[a][7]annulene yielded regio- and stereospecifically formed dibromides arising from the alkyl shift where the bromine exclusively attacks the double bond from the endo face of the double bond. DFT calculations on model compounds showed that the pyramidalization of the double bond and steric repulsion caused by the methylene protons are responsible for the stereo- and regioselective addition of bromine. 相似文献
In this study effects of anionic (sodium dodecyl sulfate, SDS), cationic (cetyltrimethylammonium bromide, CTAB) and nonionic (Triton X-100, TX100) micelles on the sensitivity of spectrophotometric molybdenum(VI) (Mo) determination based on the formation of a binary complex with gallic acid (GA) were investigated.
Micellar CTAB was found to enhance the formation of Mo–GA complex. SDS micelles exerted an inhibitory effect while TX100 micelles had no effect on the complex formation. By the optimization of experimental conditions, the determination limit of the method suggested in the literature was lowered from 5.2 × 10−5 to 4.6 × 10−6 and to 5.7 × 10−7 M, in the absence and presence of CTAB, respectively.
The mechanism of the effect of CTAB was investigated by spectrophotometric titrations and it was concluded that CTAB did not form a ternary complex with Mo and GA. The stoichiometry of the complex, deduced from the results of spectrophotometric titrations, provided evidence for the formation of para-Mo7O46− polyanions at pH 4.5, indicating to the formation of a charge transfer complex between these ions and GA in micellar medium. 相似文献
The proposed method for ascorbic acid: AA (Vitamin C) determination is based on the oxidation of AA to dehydroascorbic acid with the CUPRAC reagent of total antioxidant capacity assay, i.e., Cu(II)-neocuproine (Nc), in ammonium acetate-containing medium at pH 7, where the absorbance of the formed bis(Nc)-copper(I) chelate is measured at 450 nm. The flavonoids (essentially flavones and flavonols) normally interfering with the CUPRAC procedure were separated with preliminary extraction as their La(III) chelates into ethylacetate (EtAc). The Cu(I)-Nc chelate responsible for color development was formed immediately with AA oxidation. Beer's law was obeyed between 8.0 × 10−6 and 8.0 × 10−5 M concentration range, with the equation of the linear calibration curve: A450 nm = 1.60 × 104C (mol dm−3) − 0.0596. The relative standard deviation (R.S.D.) in the analysis of N = 45 synthetic mixtures containing 1.25 × 10−2 mM AA with flavonoids was 5.3%. The Cu(II)-Nc reagent is a lower redox-potential and therefore more selective oxidant than the Fe(III)-1,10-phenanthroline reagent conventionally used for the same assay. This feature makes the proposed method superior for real samples such as fruit juices containing weak reductants such as citrate, oxalate and tartarate that may otherwise produce positive errors in the Fe(III)-phen method when equilibrium is achieved. The developed method was applied to some commercial fruit juices and pharmaceutical preparations containing Vitamin C + bioflavonoids. The findings of the developed method for fruit juices and pharmaceuticals were statistically alike with those of HPLC. The proposed spectrophotometric method was practical, low-cost, rapid, and could reliably assay AA in the presence of flavonoids without enzymatic procedures open to interferences by enzyme inhibitors. 相似文献
Heating hydrous manganese (II) hydroxide gel at 85 °C for 12 hours produces Mn3O4 nanoparticles. They were characterized by X-ray powder diffraction (XRD) and infrared spectroscopy (FTIR). The particle size
estimated from the SEM and X-ray peak broadening is approximately 32 nm, showing them to be nanocrystalline. EPR measurements
confirm a typical Mn2+signal with a highly resolved hyperfine structure.
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The molecular geometry and vibrational frequencies of 1-(thiophen-2-yl-methyl)-2-(thiophen-2-yl)-1H-benzimidazole (C(16)H(12)N(2)S(2)) in the ground state has been calculated using the Hartree-Fock (HF) and density functional method (B3LYP) with 6-31G(d) basis set. The optimized geometric bond lengths and bond angles obtained by using HF and DFT (B3LYP) show the best agreement with the experimental data. Comparison of the observed fundamental vibrational frequencies of 1-(thiophen-2-yl-methyl)-2-(thiophen-2-yl)-1H-benzimidazole (C(16)H(12)N(2)S(2)) and calculated results by density functional B3LYP and Hartree-Fock methods indicate that B3LYP is superior to the scaled Hartree-Fock approach for molecular vibrational problems. 相似文献