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Metal Analyses (metal + analysis)
Selected AbstractsComparison of Structural and Chemical Properties of Black and Red Human Hair Melanosomes,PHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 1 2005Yan Liu ABSTRACT Melanosomes in black and red human hair are isolated and characterized by various chemical and physical techniques. Different yields of 4-amino-hydroxyphenolanaline by HI hydrolysis (a marker for pheomelanin) and pyrrole-2,3,5-tricarboxylic acid by KMnO4/H+ oxidation (a marker for eumelanin) indicate that the melanosomes in black hair are eumelanosomes, whereas those in red hair are mainly pheomelanosomes. Atomic force microscopy reveals that eumelanosomes and pheomelanosomes have ellipsoidal and spherical shapes, respectively. Eumelanosomes maintain structural integrity upon extraction from the keratin matrix, whereas pheomelanosomes tend to fall apart. The black-hair eumelanosomes have an average of 14.6 ± 0.5% amino acids content, which is attributed to the internal proteins entrapped in the melanosomes granules. The red-hair melanosomes contain more than 44% of amino acid content even after extensive proteolytic digestion. This high content of amino acids and the poorly reserved integrity of red-hair melanosomes suggest that some proteins are possibly covalently bonded with the melanin constituents in addition to those that are entrapped inside the melanin species. Soluene solubilization assay indicates the absorbance of melanin per gram of sample, adjusted for the amino acid content, is a factor of 2.9 greater for the black-hair melanosomes than the red-hair melanosomes. Metal analysis reveals significant amounts of diverse heavy metal ions bound to the two types of melanosomes. The amount of Cu(II) and Zn(II) are similar but Fe(III) content is four times higher in the red-hair melanosomes. 13C solid-state nuclear magnetic resonance spectra and infrared spectra are presented and are shown to be powerful techniques for discerning differences in the amino acid contents, the 5,6-dihydroxyindole-2-carboxylic acid:5,6-dihydroxyindole ratio, and the degree of cross-linking in the pigment. Excellent agreement is observed between these spectral results and the chemical degradation data. [source] Magnetic investigation of heavy metals contamination in urban topsoils around the East Lake, Wuhan, ChinaGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 2 2007Tao Yang SUMMARY Magnetic measurements and heavy metal analyses were performed on 133 samples from the urban soils around the East Lake in Wuhan, China. Samples were collected from four areas with different environmental settings: a heavy industrial area well known for thermal power generation and steel works; villages located in the downwind area of the industrial area; a main road with heavy traffic and roads around the East Lake. Results show that concentrations of magnetic particle and heavy metals in urban topsoils are significantly elevated due to the input of coarser-grained magnetite from industrial (e.g. power generation and steel production) and other anthropogenic activities (e.g. vehicle emissions). Concentration-related magnetic parameters, for example, magnetic susceptibility, saturation isothermal remanent magnetization and anhysteretic remanent magnetization, significantly correlate with the concentration of heavy metals. Moreover, in terms of grain sizes, the magnetic particles of different origins can be efficiently discriminated at the studied region. Therefore, magnetic measurements provide a basis for discrimination and identification of different contamination sources, and can be used as an economic alternative to chemical analysis when mapping heavy metal contamination in urban soil around the East Lake region, Wuhan, China. [source] Grafting of Molecularly Ordered Mesoporous Phenylene-Silica with Molybdenum Carbonyl Complexes: Efficient Heterogeneous Catalysts for the Epoxidation of OlefinsADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 10 2010Abstract Arenetricarbonyl complexes, or the general formula C6H4Mo(CO)3, were incorporated into crystal-like mesoporous phenylene-silica by liquid-phase deposition of molybdenum hexacarbonyl [Mo(CO)6]. By adjusting the reaction conditions, different molybdenum loadings of 1.5 and 5.9,wt% were obtained, which correspond to 3% and 14% of the phenylene contents. The texture properties of the materials as well as the nature of the surface-fixed complexes were characterized by powder X-ray diffraction, transmission electron microscopy (TEM), N2 adsorption, FT-IR, UV-vis and MAS (13C, 29Si) NMR spectroscopy. The derivatized organosilicas were examined as catalyst precursors for the liquid-phase epoxidation of cis -cyclooctene, 1-octene, trans -2-octene and (R)-(+)-limonene at 55,°C, using tert -butyl hydroperoxide as the oxidant. For each olefin the corresponding epoxide was the only product detected. In the case of cyclooctene, the intrinsic reaction rates per surface molybdenum atom were similar for both Mo loadings (TOF,1150 mol,molMo,1,h,1), suggesting that the resultant materials act as single site epoxidation catalysts. Leaching tests and metal analyses of reaction solutions showed that the catalytic activity stemmed from the immobilized species and not from the leaching of active species into solution. The oxidation of limonene gave limonene oxide as the only product in 95% yield at 3,h, which reveals an outstanding regioselectivity to the epoxidation of the endocyclic double bond. [source] Influence of stability on the acute toxicity of CdSe/ZnS nanocrystals to Daphnia magnaENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 6 2010Heather E. Pace Abstract The acute toxicity of polymer-coated CdSe/ZnS quantum dots (QDs) to Daphnia magna was investigated using 48-h exposure studies. The principal objective was to relate the toxicity of QDs to specific physical and chemical aspects of the QD. As such, two different CdSe core diameters, 2,nm QDs (green-emitting) and 5,nm QDs (red-emitting), and two different surface coatings, polyethylene oxide (PEO) and 11-mercaptoundecanoic acid (MUA) were studied. The QDs were characterized before and after the 48-h exposure using fluorescence, ultrafiltrations (3 kDa), and inductively coupled plasma-atomic emission spectrometry (ICP-AES) metal analysis. In addition, flow field flow fractionation-inductively coupled plasma-mass spectrometry (Fl FFF-ICP-MS) was used as a more extensive characterization technique to determine particle size and composition as well as identify other potential constituents in the QD solutions. The more stable QDs (PEO) were found to be less acutely toxic than the QDs with accelerated dissolution (MUA), suggesting QD stability has significant impact on the nanoparticles' short-term toxicity. The emergence of dissolved Cd2+ in solution indicates that the toxicity of the MUA QDs is likely due to Cd poisoning, and a mass-based dose response occurred as a consequence of this mode of action. Alternatively, the PEO QDs caused acute toxicity without observed particle dissolution (i.e., no detectable metals were solubilized), suggesting an alternative mode of toxic action for these nanoparticles. Results of the present study suggest that using particle number, instead of mass, as a dose metric for the PEO QDs, produces markedly different conclusions, in that smaller core size does not equate to greater toxicity. Environ. Toxicol. Chem. 2010;29:1338,1344. © 2010 SETAC [source] | ||||||||||