CHAPTER 4: Chemistry and Activity of Selenium Dioxide and Selenite Ions

Selenium dioxide (SeO₂) and selenite ion (SeO₃²⁻) are inorganic forms of Se in the +4 oxidation state. Selenium dioxide has received attention as an effective means for oxidizing organic compounds, and SeO₃²⁻ is used widely as a nutritional supplement in animal feedstock and over-the-counter supplements for humans. In large doses SeO₃²⁻ shows promise as a chemotherapeutic agent due to its ability to form reactive oxygen species (ROS) and induce oxidative DNA damage. The general chemistry and activity of SeO₂ and SeO₃²⁻ and their relation to one another are addressed in this chapter. The activity of SeO₂ in oxidizing organic compounds is reviewed. The roles of SeO₃²⁻ as a nutritional supplement, pro-oxidant, and chemopreventive and chemotherapeutic agent are addressed along with its ability to mediate the toxic effects of heavy metals including As(iii) and Hg(ii). The dual behaviors of SeO₂ and SeO₃²⁻ as pro- and antioxidants are highlighted, especially their abilities to minimize oxidative damage by coordinating metal ions that produce ROS.