Selenium absorption

Selenium is extracted as diethyldithiocarbamate complex from the solution containing citrate and EDTA [5]. Ohta and Suzuki [6] found that only a few elements, such as copper, bismuth, arsenic, antimony, and tellurium, are also extracted together with selenium. They examined this for effects of hundredfold amounts of elements co-extracted with the selenium diethyldithiocarbamate complex. An appreciable improvement of interferences from diverse elements was observed in the presence of copper. Silver depressed the selenium absorption in the case of atomisation of diethyldithiocarbamate complex, but the interference of silver was suppressed in the presence of copper. The atomisation profile from diethyldithiocarbamate complex was identical with that from selenide. 

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. 

Hurd-Karrer, Annie M., Selenium Absorption by Plants, and Their Result-... 

A comparison of absorption of selenium by selenium-depleted rats after oral administration of sodium selenate, selenomethionine, or methyl selenocysteine (from high-selenium broccoli) found that gross absorption of selenium from methyl selenocysteine was significantly lower (85%) than from sodium selenate or selenomethionine (91%), further, true selenium absorption adjusted for urinary excretion was significantly different for methyl selenocysteine, sodium selenate, and selenomethionine, with the lowest absorption for methyl selenocysteine and the highest for selenomethionine (Finley 1998). Absorption of selenium from selenomethionine was not significantly lower than from sodium selenate. 

Silver and mercury were shown to markedly reduce the absorption of selenium in rats when the inorganic salts of these elements were given orally (Whanger, 1976). Cadmium had a lesser effect on selenium absorption, and lead had no effect. Using lettuce leaves labeled either intrinsically or extrinsically with and Se, the absorption of Se... 

Ehrenkranz, R.A., Gettner, P.A., NeDi, C.M., Sherwonit, E.A., Williams, J.E., Ting, B.T., and Janghorbani, M. (1991) Selenium absorption and retention by very-low-birth-weight infants studies with the extrinsic stable isotope tag Se. J. Pediatr. Gastroenterol. Nutr, 13, 125-133. 

Vitamin E—The metabolic roles of selenium and vitamin E overlap, so that each nutrient may replace the other to a limited extent in preventing certain types of disorders. However, there are also unique functions for each nutrient, so each must be supplied in the diet to ensure good nutrition. Furthermore, the experimental supplementation of animal feed with vitamin E resulted in an improvement in selenium absorption, and a doubling of the amount of the mineral which accumulated in the liver. ... 

Figure 8.30 Time-resolved absorbance spectrum of a human urine sample in the vicinity of the selenium absorption line at 196.026 mn (a) without correction (b) after subti-action...

Dietary Selenium, Absorption, and Mechanisms of Incorporation of Selenium into Selenoproteins... 

Selenium is readily absorbed, especially in the duodenum but also in the caecum and colon. Seleno-amino acids are almost completely absorbed selenomethionine via the gut methionine transporter and selenocysteine probably via the cysteine transporter. Both selenite and selenate are >50% absorbed, selenite more readily so than selenate, and for these forms there is competition with sulphate transport. Selenite is more efficiently retained then selenate because part of the latter is rapidly excreted into the urine. Vitamins A, E, and C can modulate selenium absorption, and there is a complex relationship between selenium and vitamin E that has not been entirely elucidated for man. A combined deficiency of both nutrients can produce increases in oxidative damage markers (malondialdehyde, Ei isoprostanes, and breath hydrocarbons) and in pathological changes that are not seen with either deficiency alone. Inorganic Se is reduced to selenide by glutathione plus glutathione reductase and is then carried in the blood plasma, bound mainly to protein in the very low-density lipoprotein fraction. Selenomethionine is partly carried in the albumin fraction. 

Comparison of the ultraviolet spectra of analogous sulfur and selenium compounds shows that there is very little difference in the absorption curves, except for a slight bathochromic shift in the case of the selenium derivatives-... 

Selenium. Selenium is determined by atomic absorption after the organoselenides are broken down with acidic persulfate and all forms of selenium have been converted to H2Se. The reduction is brought about in acidic solution of KI—SnCl2 or borohydride, and H2Se is generated by addition... 

Amorphous (vitreous) selenium, vacuum-deposited on an aluminum substrate such as a dmm or a plate, was the first photoconductor commercially used in xerography (6). It is highly photosensitive, but only to blue light (2). Its light absorption falls off rather rapidly above 550 nm. Because of the lack of photoresponse in the red or near infrared regions, selenium photoreceptors caimot be used in laser printers having He—Ne lasers (632.8 nm), or soHd-state lasers (680—830 nm). 

The possibility of preconcentration of selenium (IV) by coprecipitation with iron (III) hydroxide and lanthanum (III) hydroxide with subsequent determination by flame atomic absorption spectroscopy has been investigated also. The effect of nature and concentration of collector and interfering ions on precision accuracy and reproducibility of analytical signal A has been studied. Application of FefOH) as copreconcentrant leads to small relative error (less than 5%). S, is 0.1-0.2 for 5-100 p.g Se in the sample. Concentration factor is 6. The effect of concentration of hydrochloric acid on precision and accuracy of AAS determination of Se has been studied. The best results were obtained with HCl (1 1). 

Hexahydrobenzoyloxodedelphonine acetate (VI) was dehydrogenated by selenium at 330° and gave as chief product a hydrocarbon, b.p. 90°/0-02 mm., whose composition, ultra-violet absorption spectrum and chemical properties, so far as examined, indicate that it may be a bicyclopentenobenzene and therefore in a different category from the phenanthrene hydrocarbons yielded by the atisine group of bases. 

Tile photolysis (A = 365 nm) of 42 alone resulted in a very slow conversion to the 1,4-dithiin 259, whereas the irradiation in the presence of nor-bornene quickly produced 260 in 95% yield (88CL657).Tlierefore, the conversion of 42 to 261 (or 262) and sulfur atom should be reversible. Tlie photolysis of 263 in 3-methylpentane at 77 K yielded a mixture of 261 and 262, as suggested by the electronic spectrum, which showed two absorption maxima at 580 and 370 nm (89TL2955). Similar results were also obtained for selenium species (88CL657 89TL2955). 

The UV absorption spectrum of benzoisotellurazole is similar to those of its sulfur and selenium analogues, all absorption bands of the former being bathochromi-cally shifted relative to the latter compounds. The NMR signal of the H-3 proton... 

In 1956, the alkaloid Methylpseudolycorine (101) isolated from the King Alfred daffodil (Narcissus pseudonarcissus L.) was oxidized to the pale yellow chloride with selenium dioxide (Scheme 36). Conversion into the betaine was accomplished by aqueous ammonia to give yellow prisms of the trihydrate of Criasbetaine (100) (56JA4145, 56JA4151). The UV absorption... 

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