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.
Uranyl carboxylates are known for diverse carboxylic acids (formate, butyrate, acrylate).
Uses Uranyl acetate is extensively used as a negative stain in electron microscopy."Negative Staining" University of Oxford 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.
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(IV) acetate (U(OAc)4).
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."Health Safety & Wellbeing. Uranyl acetate and uranyl nitrate" Monash University 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:Yamaguchi K, Suzuki K, Tanaka K (2010) Examination of electron stains as a substitute for uranyl acetate for the ultrathin sections of bacterial cells. J Electron Microsc (Tokyo) 59:113–118 neodymium acetate,Hosogi N, Nishioka H, Nakakoshi M (2015) Evaluation of lanthanide salts as alternative stains to uranyl acetate. Microscopy (Oxf) 64:429–435 platinum blue,Inaga S, Katsumoto T, Tanaka K, Kameie T, Nakane H, Naguro T (2007) Platinum blue as an alternative to uranyl acetate for staining in transmission electron microscopy. Arch Histol Cytol 70:43–49 hafnium chloride,Ikeda K, Inoue K, Kanematsu S, Horiuchi Y, Park P (2011) Enhanced effects of nonisotopic hafnium chloride in methanol as a substitute for uranyl acetate in TEM contrast of ultrastructure of fungal and plant cells. Microsc Res Tech 74:825–830 and oolong tea extracts.Sato S, Adachi A, Sasaki Y, Ghazizadeh M (2008) Oolong tea extract as a substitute for uranyl acetate in staining of ultrathin sections. J Microsc 229:17–20He X, Liu B (2017) Oolong tea extract as a substitute for uranyl acetate in staining of ultrathin sections based on examples of animal tissues for transmission electron microscopy. J Microsc 267:27–33
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