Determination of selenium sulfide using 1,3-dibromo-5,5-dimethylhydantoin (DBH). Analytical methods of pharmacopeias with DBH in respect to environmental and economical concern Part 11.
USP 2000 (The United States Pharmacopeia, Rockville, MD, 24th ed., 2000, pp. 1514-1515) and PH. EUR. 1997 (European Pharmacopoeia, 3rd ed., Council of Europe, Strasbourg, 1997, p. 1459) dissolve selenium sulfide by boiling with fuming nitric acid for about 1 h. After cooling to room temperature and dilution with water nitrous acid and nitrogen oxides are removed with urea also by boiling before the iodometric titration is performed. This method can be importantly simplified and improved, when using 1,3-dibromo-5,5-dimethylhydantoin (DBH) in glacial acetic acid in presence of solid potassium bromide. Selenium sulfide is dissolved during 5-10 min at room temperature. The excess of DBH and bromine can be removed with 5-sulfosalicylic acid also without boiling. The point of the indicator change for the iodometric titration is improved in comparison to the method of the pharmacopeias, because the colloidal solution of selenium mostly coagulates. Also the sulfur content of selenium sulfide can be determined with DBH.
High-efficient photocatalytic treatment of dye and anti-bacterial activity via electrochemically synthesized SeS2 nanoparticles
Selenium sulfide (SeS2) nano photocatalyst was prepared by a facile electrochemical method and characterized by XRD, scanning electron microscope, Energy dispersive X-ray analysis and IR spectroscopy. The XRD showed that SeS2 is amorphous and has an average crystallite size of 41.26 nm which has a triclinic structure. The photocatalytic activity of the sample was evaluated by the degradation of textile dye indigo carmine in aqueous solutions under ultraviolet radiation. The photocatalytic decolourization of the dye follows first-order kinetics. High efficiency was achieved at a very low concentration of 0.003 g of SeS2 nanoparticle. Easy separation from suspension by spontaneous sedimentation and reusability of the catalyst make these photocatalysts suitable for waste water treatment. Evidently, the anti-bacterial activity of SeS2 is considerable compared with the standard drug. GRAPHICAL ABSTRACT
O-Methylation effect on the carbon-13 nuclear magnetic resonance signals of ortho-disubstituted phenols and its application to structure determination of new phthalides from Aspergillus silvaticus.
The O-methylation effect on the carbon-13 nuclear magnetic resonance chemical shifts of ortho-disubstituted phenols was investigated. In phenols with nonconjugated ortho-disubstituents (1-10), O-methylation caused a downfield shift by an average of 5.2 ppm for the ortho-carbons (C-2 and -6), and a downfield shift by an average of 4.6 ppm for the para-carbon (C-4). These shift values are significantly different from those observed in ortho-monosubstituted and ortho-nonsubstituted phenols. This regularity is very useful for the spectral interpretation of some natural products with an ortho-disubstituted phenol group and for the determination of the position of the methoxy group in such compounds. Two new phthalides, silvaticol (15) and O-methylsilvaticol (16), were isolated along with nidulol (17) from Aspergillus silvaticus. In the course of the structure determination of these compounds, the O-methylation effects of ortho-mono-and ortho-disubstituted phenols were successfully applied to these phthalides. The structures of silvaticol and O-methylsilvaticol were determined as 6-hydroxy-4-methoxy-5-methylphthalide and 4, 6-dimethoxy-5-methylphthalide, respectively.