Osmium tetroxide biological tissue

One of the main uses of osmium tetroxide is as a biological staining agent for microscopic ceU and tissue studies. Osmium tetroxide is unique in that it both fixes and stains biological material. 

Miscellaneous. Aside from the oxidation chemistry described, only a few catalytic applications are reported, including hydrogenation of olefins (114,115), a, [3-unsaturated carbonyl compounds (116), and carbon monoxide (117) and the water gas shift reaction (118). This is so owing to the kinetic inertness of osmium complexes. A 1% by weight osmium tetroxide solution is used as a biological stain, particulady for preparation of samples for electron microscopy. In the presence of pyridine or other heterocyclic amines it is used as a selective reagent for single-stranded or open-form B-DNA (119) (see Nucleic acids). Osmium tetroxide has also been used as an indicator for unsaturated fats in animal tissue. Osmium tetroxide has seen limited if controversial use in the treatment of arthritis (120,121). 

It is particularly hazardous to the eyes because of its ready reaction with organic matter, a property exploited in electron microscopy in order to stain and fix biological tissues. Although osmium is a d8 transition metal, its tetroxide is a coordinatively unsaturated 16-electron species and has a tetrahedral structure3. It is highly soluble in carbon tetrachloride (375 g/ 100 g), less so in benzene, and moderately soluble in water (7.24 g/100 g). 

---