Selenium redox properties

No new calculations were specifically devoted to this heterocylic system since CHEC-II(1996). Redox properties of chalcogeno-ureas possessing this heterocyclic skeleton and resulting from the reaction of Arduengo carbenes such as 108 with sulfur or selenium was investigated through semi-empirical calculations <2000EJI1935>. 

Selenium (masses 74, 76, 77, 78, 80, and 82 Table 1) and chromium (masses 50, 52, 53 54 Table 1) are treated together in this chapter because of their geochemical similarities and similar isotope systematics. Both of these elements are important contaminants in surface and ground water. They are redox-active and their mobility and environmental impact depend strongly on valence state and redox transformations. Isotope ratio shifts occur primarily during oxyanion reduction reactions, and the isotope ratios should serve as indicators of those reactions. In addition to environmental applications, we expect that there will be geological applications for Se and Cr isotope measurements. The redox properties of Se and Cr make them promising candidates as recorders of marine chemistry and paleoredox conditions. 

The unique redox properties and ability to react with the cellular nucleophiles are influential in the catalytic and biological activities of organoselenium compounds, including those where selenium is a part of the heterocyclic ring. Selenazines,... 

Trigonal, metallic selenium has been investigated as photoelectrode for solar energy conversion, due to its semiconducting properties. The photoelectrochemistry of the element has been studied in some detail by Gissler [35], A photodecomposition reaction of Se into hydrogen selenide was observed in acidic solutions. Only redox couples with a relatively anodic standard potential could prevent dissolution of Se crystal. 

Ebselen (2-phenyl-1,2-benzisoselenazol-3(2//)-one), 4 and some of its derivatives mimic the action of GSH-Px.The sulfur analogue is completely inactive, an observation which highlights the importance of selenium in this redox chemistry. Ebselen has also been shown to be a nitric oxide synthase (NOS) inhibitor,to induce cytokines such as interferons, tumour necrosis factor, interleukin-2 and gratunocytemacrophage colony stimulating factor. These properties combined with Ebselen s low toxicity have led to interest in its therapeutic potential for a number of diseases.5... 

Inorganic pollutants include (a) cationic heavy metals such as lead, cadmium, and nickel, (b) anionic metals and inorganics such as arsenic, chromium, selenium, nitrate and fluoride, and (c) radionuclides such as strontium and uranium. The geochemistry of these pollutants can widely vary and it depends on the specific pollutant type and soil/sediment properties. The speciation and transport of these pollutants also depend on the dynamic changes in the pH and redox potential of the soil that occurs under applied electric potential. The dominant transport process... 

---