Selenium

About: Selenium is a research topic. Over the lifetime, 21192 publications have been published within this topic receiving 429715 citations. The topic is also known as: Se & selen.

Selenium and selenoproteins in the brain and brain diseases

Abstract: Over the past three decades, selenium has been intensively investigated as an antioxidant trace element. It is widely distributed throughout the body, but is particularly well maintained in the brain, even upon prolonged dietary selenium deficiency. Changes in selenium concentration in blood and brain have been reported in Alzheimer's disease and brain tumors. The functions of selenium are believed to be carried out by selenoproteins, in which selenium is specifically incorporated as the amino acid, selenocysteine. Several selenoproteins are expressed in brain, but many questions remain about their roles in neuronal function. Glutathione peroxidase has been localized in glial cells, and its expression is increased surrounding the damaged area in Parkinson's disease and occlusive cerebrovascular disease, consistent with its protective role against oxidative damage. Selenoprotein P has been reported to possess antioxidant activities and the ability to promote neuronal cell survival. Recent studies in cell culture and gene knockout models support a function for selenoprotein P in delivery of selenium to the brain. mRNAs for other selenoproteins, including selenoprotein W, thioredoxin reductases, 15-kDa selenoprotein and type 2 iodothyronine deiodinase, are also detected in the brain. Future research directions will surely unravel the important functions of this class of proteins in the brain.

An Advanced Selenium–Carbon Cathode for Rechargeable Lithium–Selenium Batteries

Abstract: The rapidly developing market for mobile electronics and hybrid electric vehicles (HEVs) has prompted the urgent need for batteries with high energy density, long cycle life, high efficiency, and low cost. Recently, rechargeable lithium-sulfur (Li–S) batteries have attracted considerable attention because of their high theoretical gravimetric (volumetric) energy density of 2570 Wh kg 1 (2200 Whl ), and low cost. However, the use of S as cathode material for Li–S batteries suffers from two major issues. One is the insulating nature of S, which results in low active-material utilization and limited rate capability. The other is the formation of electrolytesoluble polysulfides; these polysulfide intermediates, which are generated in the discharge/charge process, dissolve in the electrolyte and migrate to the Li anode, a process known as the shuttle effect. Consequently, the S cathode suffers a significant loss of S during cycling, resulting in a rapid capacity decrease. Many strategies have been used to address these problems, such as the impregnation of S into various conductive porous matrixes, surface coating of S, and the use of suitable electrolytes and additives. Although remarkable improvements have been achieved, the application of Li–S batteries is still hindered by the intrinsic drawbacks of S. Therefore, it is of great importance to explore and develop new high-energy cathode materials with improved electronic conductivity and cycling stability, to cover the shortfalls of S and provide alternative choices for practical applications. From this perspective, selenium, an element belonging to the same group in the periodic table as sulfur, is a prospective candidate for cathode materials. Although Se has a lower theoretical gravimetric capacity (675 mAhg ) than S (1675 mAh g ), its higher density (ca. 2.5 times that of S) offsets the deficiency and provides a high theoretical volumetric capacity density (3253 mAh cm ), comparable to that of S (3467 mAh cm ). It has been reported that Li–Se batteries deliver a high output voltage, so Li–Se batteries are also expected to have a high volumetric energy density. It is known that for applications in portable devices and HEVs, volumetric energy density is more important than gravimetric energy density because of the limited battery packing space. Moreover, the electronic conductivity of Se (1 10 3 Sm ) is considerably higher than that of S (5 10 28 Sm ), which suggests that Se could have higher utilization rate, better electrochemical activity, and faster electrochemical reaction with Li. Therefore, the advantages of Se promise an attractive alternative cathode material for building high-energy batteries for specific applications, including consumer electronics and transportation. However, at present, research on Li–Se batteries is still at a very early stage. Recently, Abouimrane et al. conducted pioneering work on the use of Se as a cathode material. The results show that, even bulk Se has an active material utilization of ca. 45% upon cycling, which is not commonly observed in Li–S batteries with a bulk S cathode. This suggests that Se cathode has a much better activity and a weaker shuttle effect than S. Nevertheless, bulk Se cannot completely deliver the theoretical capacity. Moreover, given the weak interaction between bulk Se and the conductive substrate, the polyselenide species generated during the Li uptake/release process cannot be effectively restrained on the cathode side. Thus, the shuttle effect of Se is not eliminated, which deteriorates the cycling performance of the Se cathode. To address these issues, encapsulation of Se molecules into a conductive porous carbon matrix may greatly improve the electrochemical performance of Se. However, this assumption has not yet been demonstrated, and the mechanism of the electrochemical reaction between Se molecules and Li remains unclear to date. Herein, we report a Se composite cathode material, in which Se is confined as cyclic Se8 molecules in the mesopores of an ordered mesoporous carbon (CMK-3) matrix. When assembled into Li–Se batteries with the water-soluble binder sodium alginate (SA), the Se/CMK-3 composite exhibits novel electrochemical behavior with a single plateau in the discharge/charge process. Data from ex situ Raman and X-ray diffraction (XRD) analysis suggest that this behavior is due to the conversion of cyclic Se8 molecules into chain-like Sen molecules in the carbon channels. Given the high electrochemical activity of the chain-like Sen molecules and the strong interaction between them and the carbon mesopores, this Se cathode shows a high capacity that approaches the theoretical value of Se, and exhibits favorable capacity retention upon cycling. The Se/CMK-3 composite was synthesized through a facile melt-diffusion process from a ball-milled mixture of [*] C.-P. Yang, S. Xin, Dr. Y.-X. Yin, H. Ye, J. Zhang, Prof. Y.-G. Guo CAS Key Laboratory of Molecular Nanostructure and Nanotechnology, and Beijing National Laboratory for Molecular Sciences, Institute of Chemistry, Chinese Academy of Sciences (CAS) Beijing 100190 (P. R. China) E-mail: ygguo@iccas.ac.cn

Selenium environmental cycling and bioavailability: a structural chemist point of view

Abstract: Selenium is usually known as the ‘double-edged sword element' for its dual toxic and beneficial character to health. Since the pioneer works by Schwarz and Foltz on the relationships between selenium deficiency and liver, muscle and heart diseases, many efforts have been undertaken to better understand the role of selenium in health. At the same time, an increasing number of publications have appeared during these last years on the selenium physico–chemical interactions within the environment. Both types of research represent ongoing efforts to correctly estimate the bioavailability of selenium species for health and the environment. Redox reactions, diffusion, adsorption and precipitation processes or interactions with organic matter and biota govern the speciation and mobility of selenium in the environment. This review intends to emphasize and collect the important advances made during these last years in the mechanistic understanding of processes which govern selenium cycling and bioavailability, like adsorption at the mineral/water interface, precipitation of elemental selenium, or bioavailability of nanoscaled precipitates. The advent of powerful spectroscopic techniques, like X-ray absorption spectroscopy, has allowed the structural description of adsorption and substitution processes that selenium undergoes in a variety of minerals. These and other structural details about selenium precipitates are reviewed here, together with their relationships to the bioavailability of the element in the environment.

Regulation of Selenium Metabolism and Transport

Abstract: Selenium is regulated in the body to maintain vital selenoproteins and to avoid toxicity. When selenium is limiting, cells utilize it to synthesize the selenoproteins most important to them, creating a selenoprotein hierarchy in the cell. The liver is the central organ for selenium regulation and produces excretory selenium forms to regulate whole-body selenium. It responds to selenium deficiency by curtailing excretion and secreting selenoprotein P (Sepp1) into the plasma at the expense of its intracellular selenoproteins. Plasma Sepp1 is distributed to tissues in relation to their expression of the Sepp1 receptor apolipoprotein E receptor-2, creating a tissue selenium hierarchy. N-terminal Sepp1 forms are taken up in the renal proximal tubule by another receptor, megalin. Thus, the regulated whole-body pool of selenium is shifted to needy cells and then to vital selenoproteins in them to supply selenium where it is needed, creating a whole-body selenoprotein hierarchy.

The requirement and toxicity of selenium in rainbow trout (Salmo gairdneri).

Abstract: This study measured the dietary selenium requirement of rainbow trout and their response to excessive levels of dietary selenium. A dietary selenium level of 0.07 microgram/g dry feed with a waterborne selenium level of 0.4 +/- 0.2 microgram/liter and a dietary vitamin E level of 0.4 IU/g dry diet was sufficient to prevent frank selenium deficiency symptoms. Maximal plasma GSH.px activity was obtained at a dietary selenium level between 0.15 and 0.38 microgram/g dry feed which is less than the average selenium concentration of commercial diets. Chronic dietary selenium toxicity occurred at 13 microgram selenium/g dry feed. Major effects of selenium toxicity were reduced growth rate, poor feed efficiency and a high number of mortalities. No histopathological lesions or significant deviation in the investigated blood parameters or liver somatic index were detected in trout raised on diets containing 13 microgram selenium/g dry feed. Tissue selenium analysis indicated that trout can maintain homeostasis with dietary selenium levels up to 1.25 microgram/g dry feed. The selenium uptake and accumulation in tissues of trout reared on diets containing in excess of 3 microgram/g dry feed may ultimately be toxic to trout if maintained over long periods of time.