Selenium sources for

Selenoureas <90JOC2567> and selenones (derived from a phosphorus yUde and selenium) <92TLI333> can also act as selenium sources for addition across triple bonds (Scheme 11). 

Scholes and co-workers utilised TBPSe as selenium source for the synthesis of CISe nanoparticles. In a typical reaction, the TBPSe precursor was rapidly injected to the reaction mixture composed of Cul, In(02CCH3)3 dissolved in DDT, ODE and OA at 200 °C. Initially, the metal salts react with DDT to form [Cu-In-(S-R)x] clusters as an intermediate which upon... 

Practical applications [2] of a GammaMat M model using the new Selenium crawler camera loaded with approx. 1 TBq (30Ci) on a pipeline of diameter 12 and wall thickness of 0.25 showed 6-7 m axial distance to the exposed source as limit of the radiation controlled area (40pSv/h) and 22m perpendicular to the pipeline. Other authors [3] have reported about a comparison for Ir-192 and Selenium source on a 4.5 diameter pipe and 0,125 steel thickness they have found for 0.7 Tbq (18Ci) Selenium a value of 1 Om behind the film (in the unshielded beam) comparing under same conditions to approx. 40m for Iridium. 

Aerosol concentrations in excess of 4.0 jag Se/m3 are potentially harmful to human health (Harr 1978). Concentrations in excess of this value (6.0 pg Se/m3) were regularly encountered in the vicinity of the smeltery at Sudbury, Ontario, Canada (Nriagu and Wong 1983). It is not now known whether respiration rates of wildlife, particularly birds, are comparable to those of humans, whether selenium absorption energetics are similar, or whether wildlife species that frequent point sources of air contaminated by high selenium levels for protracted periods are at greater risk than humans. Until additional and more conclusive data become available, aerosol concentrations of less than 4.0 pg Se/m3 are recommended for the protection of sensitive wildlife species. 

Free electron pairs are a good source for an electron which is to be ejected and therefore, the IE of ethanol and dimethylether is lower than that of ethane. It has been shown that the IE of a poly-substituted alkane is almost the same as the IE of the structurally identical mono-substituted alkane which has the lowest value. [27] The other substituent, provided it is separated by at least two carbon atoms, exerts a very small effect upon the IE, e.g., the IE of dimethylsulfide, CH3SCH3, 8.7 eV, is almost the same as that of methionine, CH3SCH2CH2CH(NH2)COOH. Introduction of an oxygen decreases the IE less than nitrogen, sulfur or even selenium do, since these elements have lower electronegativities and thus, are even better sources of an electron. 

Peroxidases (E.C. 1.11.1.7) are ubiquitously found in plants, microorganisms and animals. They are either named after their sources, for example, horseradish peroxidase and lacto- or myeloperoxidase, or akin to their substrates, such as cytochrome c, chloro- or lignin peroxidases. Most of the peroxidases studied so far are heme enzymes with ferric protoporphyrin IX (protoheme) as the prosthetic group (Fig. 1). However, the active centers of some peroxidases also contain selenium (glutathione peroxidase) [7], vanadium (bromoperoxidase)... 

In contrast, the analogous diethyl-diselenocarbamates (dsc) have been shown to be poor sources for the deposition of ZnSe or CdSe films. Under similar reaction conditions (10 -10 Torr, 370-420° C) the diethyl dsc precursors give films of the metal selenide heavily contaminated with selenium [108]. However the mixed alkyl dsc complex Eq. 4 have been used successfully to deposit thin films of CdSe or ZnSe [109,110]. 

Hopke, et al. (4) and Gaarenstroom, Perone, and Moyers (7) used the common factor analysis approach in their analyses of the Boston and Tucson area aerosol composition, respectively. In the Boston data, for 90 samples at a variety of sites, six common factors were identified that were interpreted as soil, sea salt, oil-fired power plants, motor vehicles, refuse incineration and an unknown manganese-selenium source. The six factors accounted for about 78 of the system variance. There was also a high unique factor for bromine that was interpreted to be fresh automobile exhaust. Large unique factors for antimony and selenium were found. These factors may possibly represent emission of volatile species whose concentrations do not oovary with other elements emitted by the same source. 

Chemical deposition of both M0S2 and MoSei has been reported from ammonium molybdate solution [76,77], For the sulphur and selenium sources, thioacetamide and selenosulphate were used, respectively. Ammonium hydroxide was added to the sulphide solution, while an acetic acid/ammonium acetate buffer was used with the selenide solution (pH values were not given). Reducing agents (either hydrazine [76] or sodium dithionite [77]) were added to the baths. Deposition was started at 90-100°C, followed by lowering to room temperature. 

Carbon monoxide serves as the sole carbon and energy source for the carboxydo bacteria under aerobic conditions. Using water as the oxygen donor, carbon monoxide oxidase catalyzes the hydroxylation of carbon monoxide, giving carbon dioxide or bicarbonate for assimilation. Most work has been carried out on the enzyme from Pseudomonas carboxydovorans.,ftJ7>W38 The activity of carbon monoxide oxidase is considerably stimulated upon anaerobic treatment with sulfide and dithionite, or by aerobic treatment with selenite. The binding of selenite to the oxidase specifically activates the CO — methylene blue reaction.1039 The molybdenum cofactor liberated from selenium-activated carbon monoxide oxidase does not contain selenium. Here, then, the... 

The many diverse components of milk have demonstrable effects on human health. Perhaps, the most commonly associated component of dairy food is that of dietary calcium. Dairy products provide the most significant contribution to dietary calcium intake in the modem Western diet. It has been estimated that dairy products contribute to >72% of dietary calcium in the United States (Huth et al., 2006). Calcium is an important mineral for maintenance of optimal bone health (Bonjour et al., 2009) and is an integral component of key metabolic pathways relating to, for example, muscle contraction both in skeletal and smooth muscle (Cheng and Lederer, 2008). Further, dairy products contribute other essential nutrients in the diet, such as proteins, phosphorus, potassium, zinc, magnesium, selenium, folate, riboflavin, vitamin B12, and vitamin A (Haug et al., 2007 Huth et al., 2006). Low-fat milk alternatives are fortified with vitamin A and vitamin D which is added to milk and fermented milk in many countries making it an important source for vitamin D (Huth et al., 2006). 

Gross necropsy lesions of a selenium deficiency are identical to those of a vitamin E deficiency (NRC, 1994) and include exudative diathesis and myopathy of the gizzard. Paleness and dystrophy of the skeletal muscles (white muscle disease) are also common. The incidence and degree of selenium deficiency may be increased by environmental stress. Selenium is generally included in trace mineral premixes. Common sources for supplementation of poultry diets are sodium selenite and sodium selenate. Selenium yeast is also used in conventional diets. 

Vitamin E is required for normal growth and reproduction. The most important natural source is a-tocopherol found in plant oils and seeds. The ester form (e.g. vitamin E acetate) can be synthesized and is used for feed supplementation. One international unit is defined as being equivalent to the activity of 1 mg DL-a-tocopherol acetate. The nutritional role of vitamin E is closely interrelated with that of selenium and is involved mainly in the protection of lipid membranes such as cell walls from oxidative damage. Although these signs are similar to those of selenium deficiency, it is not possible to substitute selenium completely for vitamin E. Both nutrients are required in the diet. 

For some elements such as arsenic and selenium, which have their main atomic absorption wavelengths lying on the edge of the vacuum UV, the performance of hollow cathode lamps is often poor, the lamps displaying low intensity and poor stability. This, plus the search for more intense sources for AFS (see Chapter 1, section 10), resulted in the development of microwave-powered electrodeless discharge lamps (EDLs) as spectral line sources towards the end of the 1960s.3-5... 

Also widely employed are organoselenium compounds containing group 14 elements. Phenyl trimethylsilyl selenide 102 can be easily prepared from diphenyl diselenide 8 and is a good source for selenium nucleophiles (Scheme 24). In the presence of methanol selenols are generated for use in Michael reactions or in ring-... 

Other areas of selenium chemistry, such as selenium rings, selenides, " organoselenium compounds, " and the focus of older, more comprehensive accounts of Se halide chemistry will not be covered here. Additionally, the vast environmental chemistry of selenium, for example, its aqueous and sediment speciation, plant uptake, nutritional and human health aspects, and appearance in coafl and coal-derived ash, are beyond the scope of this review. The previous reviews on Se-containing ligands, " biochemistry of selenium,as well as other relevant aspects, remain some of the most valuable sources for information on these subjects. 

One of the synthetic procedures of metal complexes of type 53 is the reaction of metal-carbene complexes with selenium sources such as alkyneselenolates [109]. The stability of selenobenzaldehyde is enhanced by coordinating to metal carbonyls, and the reactivity of the complexes has been studied [110]. For example, the selenobenzaldehyde complexes reacts with methylthiohexyne even at - 30 °C to afford another type of complex where the selenium atom of the selenocarbonyl group is still coordinated to the metal (Eq. 29) [llOd]. 

Thompson M., Pahlavanpour B., Walton S. J. and Kirkbright G. F. (1978) Simultaneous determination of trace concentrations of arsenic, antimony, bismuth, selenium and tellurium in aqueous solution by introduction of the gaseous hydrides into an ICP source for emission spectrometry, Analyst 103 568-579. 

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