Uranyl acetate

Uranyl acetate is the acetate salt of uranium oxide, a toxic yellow-green powder useful in certain laboratory tests. Structurally, it is a coordination polymer with formula UO2(CH3CO2)2(H2O)·H2O.

Structure
In the polymer, uranyl (UO22+) centers are bridged by acetate ligands. The remainder of each (heptacoordinate) coordination sphere is provided by an aquo ligand and a bidentate acetate ligand. One water of crystallization occupies the lattice.

Uses
Uranyl acetate is extensively used as a negative stain in electron microscopy. Most procedures in electron microscopy for biology require the use of uranyl acetate. Negative staining protocols typically treat the sample with 1% to 5% aqueous solution. Uranyl acetate staining is simple and quick to perform and one can examine the sample within a few minutes after staining. Some biological samples are not amenable to uranyl acetate staining and, in these cases, alternative staining techniques and or low-voltage electron microscopy technique may be more suitable.

1% and 2% uranyl acetate solutions are used as an indicator, and a titrant in stronger concentrations in analytical chemistry, as it forms an insoluble salt with sodium (the vast majority of sodium salts are water-soluble). Uranyl acetate solutions show evidence of being sensitive to light, especially UV, and will precipitate if exposed.

Uranyl acetate is also used in a standard test—American Association of State Highway and Transportation Officials (AASHTO) Designation T 299—for alkali-silica reactivity in aggregates (crushed stone or gravel) being considered for use in cement concrete.

Uranyl acetate dihydrate has been used as a starting reagent in experimental inorganic chemistry.

Related compounds
Uranyl carboxylates are known for diverse carboxylic acids (formate, butyrate, acrylate).

Safety
Uranyl acetate is both chemically toxic and mildly radioactive. Chronic-exposure effects may cumulate.

In general, uranium salts exhibit nephrotoxicity. Normal commercial stocks from depleted uranium have typical specific activity 0.37 - 0.51 μCi/g, too weak to harm from outside the body. However, uranyl acetate is very toxic if ingested, inhaled as dust, or absorbed through cut or abraded skin.

Microbiologists have developed a number of alternative stains: neodymium acetate, platinum blue, hafnium chloride, and oolong tea extracts.