Relationship between selenium and

Whanger, P Oregon State University Role of selenium and vitamin E in scour and immunity of newborn calves influence of pregnancy on selenium metabolism in women of low selenium status metabolic relationship between selenium and myopathy CRIS/UDSA 2001... 

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. 

Ohlendorf, H.M., R.L. Hothem, C.M. Bunck, T.W. Aldrich, and J.F. Moore. 1986a. Relationships between selenium concentrations and avian reproduction. Trans. North Amer. Wildl. Nat. Resour. Conf. 51 330-342. 

The metallic properties observed for the d7 compounds listed in Table I are also consistent with the Goodenough model. The rhodium-selenium system is of particular interest and demonstrates clearly the important relationships between structure and transport properties. Cations may be removed from the superconducting compound (Tc = 6°K), RhSe2. The pyrite structure is maintained as the eg band is gradually emptied, and at the composition Rh2/3Se2 (RhSe3), all cations are trivalent—i.e., have the configuration 4d6. It is not known yet if the ideal... 

Figure 12.17. Relationship between selenium (Se03) sorbed and in solution for various pH values (time effects) (from Hamdy and Gissel-Nielsen, 1977, with permission).

The relationship between selenium deficiency and KD in Zhangjiakou district, China has been described in detail by Johnson et al. (2000). Soils... 

The close relationship between Se and vitamin E has a biochemical basis. Vitamin E acts to minimize damage to membranes inflicted by free radicals. Selenium (GSH peroxidase) acts to prevent the accumulation of HCXDH, which is a source of hydroxy radicals. Hydroxyl radicals can damage cell membranes, as well as other components of the cell. Damage that is more closely identified with Se than with vitamin E, such as pancreatic atrophy, may be caused by HOOH-in-flicted damage to soluble components of the cell, rather than damage to cell membranes. The converse situation also holds. For cxaniplc, vitamin E deficiency in rats produces fetal resorptions. This problem cannot be prevented by Se. 

Dhur A, Galan P, Hercberg S. 1990. Relationship between selenium, immunity and resistance against infection. Comp Biochem Physiol [C] 96(2) 271-280. 

Chapter 5 considers the relationship between mechanism and regio- and stereoselectivity. The reactivity patterns of electrophiles such as protic acids, halogens, sulfur and selenium electrophiles, mercuric ion, and borane and its derivatives are explored and compared. These reactions differ in the extent to which they proceed through discrete carbocations or bridged intermediates and this distinction can explain variations in regio- and stereochemistry. This chapter also describes the El, E2, and Elcb mechanisms for elimination and the idea that these represent specific cases within a continuum of mechanisms. The concept of the variable mechanism can explain trends in reactivity and regiochemistry in elimination reactions. Chapter 6 focuses on the fundamental properties and reactivity of carbon nucleophiles, including... 

Substiiution of one of the Y atoms of a pyramidal XYj molecule by a Z atom lowers the symmetry from Cj to C. Then the degenerate vibrations split into two bands, and all six vibrations become infrared and Raman active. The relationship between C3 and C is shown in Table II-3d. Table ll-3e lists the vibrational frequencies of pyramidal ZXY2 molecules. Simon and Paet-zold made an extensive study of the vibrational spectra of selenium compounds. The ZXYW-type molecule belongs to the C, point group, and all six vibrations are infrared and Raman active. The vibrational spectra of OSClBr and [XSnYZ] (X, Y, Z a halogen) have been reported. 

Further research is needed to elucidate the relationship between selenium status, bone metabolism and the pathogenesis of KBD. The identification of a factor and mechanism which may induce skeletal lesions in conditions of selenium deficiency, should be investigated. 

Average hair levels are up to 0.5 ppm. The relationship between hair and tissue concentrations is not well understood. The utility of hair testing is oomplioated by the widespread use of selenium in shampoos. 

A comparison of the maps of early heart mortality and cardiovascular-related deaths of different areas of the United States revealed an inverse relationship between selenium levels and the mortality pattern. ... 

The Periodic Table. Students are asked to correlate lead, mercury and selenium occurrence on the Periodic Table with airborne exposure risk. Students are asked to name the chemical, predict the common form at RT, and postulate on a potential periodic trend. The relationship between periodicity and exposure is explored. Exposure limits are found in the NIOSH Guide Book (Table V). Students learn to assess and predict from the periodic table. Future, detailed chemical education on using the Periodic Table is emphasized. 

Pyl is rare, occurring only in some ancient bacteria. Sec, containing the side chain CH2SeH, is widespread in fact, it occurs in at least two dozen human proteins that rely on the reactivity of the essential trace element selenium for their function. The pAT, for the SeH group in Sec is 5.2. (For comparison, the pATa for the SH in Cys is 8.2.) (a) Draw the structure of Sec at pH 7 compare it with that of Cys at the same pH. (b) Determine p/ for Sec. (c) Given the relationship between sulfur and selenium in the periodic table, and the pATa differences between SH and SeH, how do you expect the chemical reactivities of Sec and Cys to compare ... 

Qualified health claims for dietary supplements recognized by the FDA as part of its enforcement discretion include such examples as the relationships between phosphatidylserine and cognitive function, B vitamins and cardiovascular disease, omega-3 fatty acids and cardiovascular disease, selenium and cancer, and antioxidant vitamins and cancer. 

This parameter was determined from xerographic residual potential in a-Sei- Te monolayer films. As one can see, even with very little Te alloying, there is a considerable rise in both hole and electron deep traps. The relationship between the trapping time and the residual potential has been evaluated by several authors (see, for example. Refs. [12, 15]). It can be seen that once the Te concentration exceeds 12 wt% Te, the residual potential is more than an order of magnitude larger than typical values for pure selenium. 

To some extent the vitamin E requirement may be lessened by the presence in the diet of synthetic antioxidants and by selenium. Much evidence supports a relationship between the nutritional need for selenium and that for vitamin E. Lack of either causes muscular dystrophy in many animals as well as severe edema (exudative diathesis) in chicks. Since vitamin E-deficient rats have a low selenide (Se2 ) content, it has been suggested that vitamin E protects reduced selenium from oxidation.) Vitamin C (ascorbic acid), in turn, protects vitamin E. 

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