Tellurium biological importance

Like selenium, the process of reduction/oxidation cycling in biological systems is important and changes in the oxidation state are often an easy means of determining bioreduction for added tellurium oxyanions. The general order of... 

The hydrolysis of seleno- and telluropyrylium dyes involves nucleophilic addition of water to the substrate. a,f3-LJnsaturated selones and -tellones 60 are intermediates in this reaction (Equation 22) <1997JOC4692, 1998JOC5716>. Diketones are the primary hydrolysis products isolated in high yields from these reactions. The tellurium derivative hydrolyzes most rapidly over the pH range 3-12, with the sulfur analogue least reactive under these conditions. Seleno- and telluropyrylium dyes are important both for their biological activities and potential industrial applications (see Section 7.11.8). 

Even though the Mossbauer effect has been observed for almost 50 different elements and ca. 100 different nuclides, only a few of these elements are widely used as Mossbauer effect probes. The nuclides which are both experimentally viable and yield useful chemical information are iron-57, tin-119, antimony-121, and europium-151. More difficult to use but of importance in coordination chemistry are gold-197, nickel-61, ruthenium-99, tellurium-125, iodine-129, dysprosium-161, tungsten-182, and neptunium-237. Among these isotopes, iron-57 is by far the easiest, most informative, and most widely used nuclide in both traditional coordination chemistry and in studies of biologically significant coordination complexes. 

A number of other selenium proteins have been discovered in biological materials, but their function is not yet sufficiently known. For example, a selenium protein (17kDa) was found in rat sperm. It is interesting that high concentrations of selenium in male sexual organs are maintained in animals with selenium deficiency therefore, selenium compounds are likely to be important for reproductive function. Some anticarcinogenic effects are also attributed to this element. Selenium also reduces the toxic effects of arsenic, cadmium, mercury, thallium and tellurium. With arsenic, the mechanism of this protective effect is the formation of selenobis(S-glutathionyl)arsinium anion, which is formed in erythrocytes and excreted in bile (6-36). 

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