Selenium species

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). 

Seby F, Potin-Gautier M, Giffaut E, Borge G, Donard OFX (2001) A critical review of thermodynamic data for selenium species at 25 °C. Chem Geol 171 173-194 Ball S, Milne J (1995) Studies on the interaction of selenite and selenium with sulfur donors. Part 3. Sulfite. Can J Chem 73 716-724... 

Figure 1.93. /02-pH diagram with the stability fields of aqueous species in Na-K-H-S-Se-0 system for the conditions SS = 10 mol/kg H2O, ESe = 10 mol/kg H2O, ionic strength = 1, and temperature = 150°C. Dashed lines are the ratio ho-a i- /a i- in logarithmic units. Stability fields for native sulfur and native selenium and the boundaries between predominance regions of oxidized and reduced selenium species are omitted for clarity (Shikazono, 1978b). 

The selenium species that are drawing most attention are Se(IV) and Se(VI) in water and sediments, and the biomethylated products (dimethylselenide and dimethyldi-selenide) that are spread into the environment (Camara et al. 1995). Se-species in food (including Se-cysteine and other species in yeast) are in the limelight (Crews 1998) because of their beneficial effect on human health and their increasing use as nutraceuticals. 

This reaction depends upon the facile solvolysis of (J-haloselenides and the facile oxidative elimination of a selenoxide, which was discussed in Section 6.6.3. An alternative method, which is experimentally simpler, involves reaction of alkenes with a mixture of diphenyl diselenide and phenylseleninic acid.189 The two selenium reagents generate an electrophilic selenium species, phenylselenenic acid, PhSeOH. 

Finally, it has recently been shown207 that some silenes can add sulfur or selenium to give silathiiranes 110, as confirmed by a crystal structure, or silaseleniranes 111, respectively (Eq. 37). Only sterically crowded silenes such as 112 gave stable solid adducts, and in the case of the selenium species the adducts visibly decomposed in the solid state over a few days. 

Jackson B.P., Miller W.P. Effectiveness of phosphate and hydroxide for desorption of arsnic and selenium species from iron oxides. Soil Sci Soc Am J 2000 64 1616-1622. 

Besser, J.M., J.N. Huckins, and R.C. Clark. 1994. Separation of selenium species released from Se-exposed... 

Wiedmeyer, R.H. and T.W. May. 1993. Storage characteristics of three selenium species in water.Arch. Environ. Contamin. Toxicol. 25 67-71. 

In the lower fan areas Se concentrations were monitored up to 400 pg/L. Similar historical distribution of soil Se content and shallow groundwater content indicate that dissolved selenium species were leached from saline soils by irrigation water. The drainage discharge of shallow groundwater and subsurface irrigation water was accompanied by increasing accumulation of Se in Kesterson Reservoir. 

Cutter [122] used a selective hydride generation procedure as a basis for the differential determination of arsenic and selenium species in sediments. Goulden et al. [123] also discuss the determination of arsenic and selenium in sediments by atomic absorption spectrometry. 

Tanzer D, Heumann KG (1991) Determination of dissolved selenium species in environmental water samples using isotope dilution mass spectrometry. Anal Chem 63 1984-1989... 

The redox cycling of selenium. Underlining reflects the relative concentrations of selenium species in surface and deep waters. The preferential uptake of selenite in surface waters is indicated by a larger dissolved-to-particulate arrow. Source-. After Cutter, G. A., and K. W. Bruland (1984). Limnology and Oceanography, 29, 1179-1192. 

Scheme 2.6 An immobilized selenium species for cyclo-addition reactions.

A new cyclization strategy via PET-generated electrophilic selenium species starting from diphenyldiselenide was introduced by Pandey et al. They succeeded in the cyclization of enyne compounds in good yields in the range 50-60% as well as in synthesizing a,a -trans dialkyl cyclic ethers via diastereoselective oxyselenation of l,n-diolefins (Scheme 31) [42,43],... 

Izumi, F. (1993) Rietveld analysis program RIE-TAN and PREMOS and special applications. In Young, R.A. (ed.) The Rietveld Method, Oxford, Oxford University Press, 236-253 Jackson, B.P. Miller, W.P. (2000) Effectiveness of phosphate and hydroxide for desorption of arsenic and selenium species from iron oxides. Soil Sci. Soc. Am. J. 64 1616-1622 Jain, A. Raven, K.P. Loeppert, R.EI. (1999) Ar-senite and arsenate adsorption on ferrihy-drite Surface charge reductions and net OEI-release stoichiometry. Environ. Sci. Techn. 

On-line anion exchange LC/ICP-MS methods for selenium and chromium speciation have been published [30], In studies of selenium speciation in environmental samples LC/ICP-MS and LC/ ESI-MS methods have been used for the determination of both inorganic and organic selenium species [43]. For the determination of methyl selenide, strong anion exchange and RP chromatography have been employed [43], while for the determination of seleno-aminoacids, IP RP chromatography with on-line detection based on ICP-MS has been successfully employed [44],... 

In order to dissolve adequately all selenium species including selenium metal and selenium in steel samples, an aqua regia digestion procedure was used in lieu of the existing NIOSH extraction method. 

Figure 9.20 Different selenium species determined by HPLC-ICP-MS in leaves, stems and roots of dill (1) Se (VI) (2) Se (IV) (3) SeCys2 (4) MeSeMet (5) MeSeCys (6) SeMet. (O. Cankur, S.K.V. Yathavakilla, J.A. Caruso, Talanta, 70, 784 (2006). Reproduced by permission of Elsevier.)...

An analytical technique has been developed for the determination of selenium species in urine to identify selenium containing compounds by combining electrospray MS/MS with ICP-MS after preparative solid phase extraction and final reversed phase HPLC separation.69... 

Abdullah, M.I., Shiyu, Z. and Mosgren, K. (1995) Arsenic and selenium species in the oxic and anoxic waters of the Oslofjord, Norway. Marine Pollution Bulletin, 31(1-3), 116-26. 

Arsenic-metal complexes, characteristics, 2, 34 Arsenic-selenium species alkyne additions, 10, 782 characteristics, 12, 640 Arsenides... 

Table 14.2 presents a list of both inorganic and organoselenium species that have been identified in animals, bacteria and plants. In order to study the wide variety of selenium species in biological materials, appropriate sample pretreatment and separation methods have to be chosen. Extraction of the selenium-containing species from the sample matrix has to be complete, and the integrity... 

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