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 UO22·H2O.
Structure
In the polymer, uranyl centers are bridged by acetate ligands. The remainder of each coordination sphere is provided by an aquo ligand and a bidentate acetate ligand. One water of crystallization occupies the lattice.Uranyl carboxylates are known for diverse carboxylic acids.
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. 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 Designation T 299—for alkali-silica reactivity in aggregates being considered for use in cement concrete.
Uranyl acetate dihydrate has been used as a starting reagent in experimental inorganic chemistry.
Preparation and reactions
The compound can be prepared by treating uranium trioxide with acetic acid:The acetate ligands of uranyl acetate can be replaced to give a variety of uranyl complexes. Uranyl acetate can also be reduced by zinc to give the uranium acetate.
Safety
In general, uranium salts exhibit nephrotoxicity. Normal commercial stocks from depleted uranium have typical specific activity, 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.