Osmium exposure

Concentrations in air as low as IO7 g/ms can cause lung congestion, skin damage, or eye damage. Exposure to osmium tetroxide should not exceed 0.0016 mg/ms (8-hour time weighted average - 40-hour work week). 

Donor-acceptor complexes. A colorless hexane (or dichloromethane) solution of osmium tetraoxide upon exposure to benzene turns yellow instantaneously owing to the formation of a donor/acceptor complex,218 i.e.. 

A colourless solution of osmium tetroxide in hexane or dichloromethane upon exposure to benzene turns yellow instantaneously (Wallis and Kochi,... 

Lesion in bovine dentin with tubules protruding from degraded intertubular matrix (left degraded matrix right intact matrix). Demineralization in 0.1 M acetic acid pH 4.0, with subsequent exposure to bacterial collagenase. Fixed and demineralized with glutar-dialdehyde-acetic acid, post-fixed with osmium tetroxide ultrathin sections stained with uranyl acetate - lead citrate. 

Osmium tetroxide is poisonous by all routes of exposure. The vapor is an... 

Chemical Properties. Compound 2 is readily decarbonylated upon exposure to UV irradiation.5 Irradiated solutions of 2 readily yield addition products of sulfur containing small molecules such as COS, CS2, and H2S. In the absence of reagents it will form the hexanuclear compound Os6(CO)17(/r4-S)2. It reacts with other metal complexes to form higher nuclearity osmium clusters and heteronuclear metal cluster compounds.5,11,12... 

Contrast in the TEM increases as the atomic number of the atoms in the specimen increases. Since biological molecules are composed of atoms of very low atomic number (carbon, hydrogen, nitrogen, and so on), contrast is increased with a selective staining, obtained by exposure of the specimen to salts of heavy metals, such as uranium, lead, and osmium, which are electron opaque (www.hei.org/research/depts/aemi/emt.htm). 

The reason for it is not obvious since gold is not a very rare element on earth, and other metals, for example, platinum, rhodium, osmium, and rhenium, are less abundant and more expensive. Its yellow color cannot be the reason either, since other metals, such as copper, and its alloys as bronze or brass, have different colors from the bright silver of most of the metals. Probably, the reason resides in its noble character. In fact, gold does not tarnish with time, and coins and jewelry remain indefinitely unalterable even after long exposure to extremely aggressive conditions. 

Pyrophoric Osmium Dioxide.—The oxide prepared by reduction of alkali osmates with alcohol or by hydrolysis of ammonium chlorosmate is not pure, but contains small quantities of organic substances or alkalies. When dry it is liable to ignite upon exposure to air, and even to detonate if warmed4 to 800° C. directly it meets the air. 

Properties. Osmium tetroxide forms pale yellow crystals with a very characteristic odour (a possible description is that of a mixture of ozone and damp hay). It has a considerable vapour pressure at room temperature and so must be kept in stoppered container or (preferably) in sealed ampoules. The vapour is toxic (TLV 2.5 p.p.m.).558a The long-term occupational exposure limit (OEL) is 0.002mgm 3. 558b... 

Osmium and compounds Osmium tetroxide is a colorless to pale yellow crystalline solid with an odor that has been described as pungent or chlo-rine-like. Students and workers must take precautions in the use of osmium tetroxide. Prolonged periods of inhalation exposure to osmium tetroxide cause insomnia, digestive disturbance, and distress to the pharynx and larynx. ... 

American Conference of Governmental Industrial Hygienists (ACGIH). 1998. Osmium tetroxide. In TLVs and other occupational exposure values—1998. Cincinnati, OH ACGIH. 

Osmium tetroxide-mediated cis hydroxylation of a silyl enol ether has been demonstrated to produce the corresponding a-hydroxy ketone in moderate yield after exposure to an acidic woric-up, e.g. (64) to... 

The osmylation of arenes (Ar) with osmium tetroxide is a particularly informative system with which to illustrate the close interrelationship between the thermal and photochemical activation of electron-transfer oxidation. For example, a colorless solution of osmium tetroxide in n-hexane or dichlorometbane upon exposure to benzene turns yellow instantaneously. With durene an orange coloration develops and a clear bright red solution results from hexamethylbenzene. The quantitative effects of the dramatic color changes are illustrated in Figure 3 by the spectral shifts of the electronic absorption bands that accompany the variations in aromatic conjugation and substituents. The progressive bathochromic shift parallels the decrease in the arene ionization potentials (/F) in the order benzene 9.23 eV naphthalene... 

Osmium is dissolved by acids or by aqua regia only after long periods of exposure to the liquids. When heated, the metal combines with oxygen... 

The morphology of ruber modified epoxy photopolymers was found to depend on the cure conditions as well as the nature and concentration of rubber. The commercially available acrylonitrile-butadiene copolymer rubber modifiers with varying percentages of acrylonitrile content were used. They were polymerized using a photocationic initiator involving a UV exposure followed by a thermal cure. Transmission electron micrographs of osmium tetroxide stained specimens, coupled with dynamic mechanical measurements indicated that phase separation and particle size distribution depended not only on rubber concentration and compatibility, but also on the cure conditions. 

For standard electron microscopy, cells and tissue are postfixed in 1% osmium tetroxide for 30 min to stain the membranes. Exposure to osmium tetroxide decreases the size of the silver particles and some might even disappear (Burry et al., 1992). Reducing both the concentration of osmium to 0.1% and processing for 10 min will prevent this loss of silver particles. 

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