Osmium, colloidal

Willner I, Maidan R, Mandler D, Durr H, Dorr G, Zengerle K (1987) Photosensitized reduction of CO2 to CH4 and H2 evolution in the presence of ruthenium and osmium colloids - strategies to design selectivity of products distribution. J Am Chem Soc 109(20) 6080-6086... 

The immunoreplica technique (14) is used when it is necessary to detect antigenic sites on the plasma membrane of cultured cells. The cells are cultured on coverslips, and are fixed as described above depending on the antibody in question, and immunolabeled in situ as described in Section 3.1.1.2., steps 3-9. After immunolabeling (Section 3.1.1.2., step 9), they are further fixed with 1% osmium tetroxide and are dehydrated in a graded series of ethanol (70, 90, 100%), critically point-dried, and replicated with a layer of carbon and platinum, The replicas are cleaned with sodium hypochlorite and chronic acid before examination with the transmission electron microscope. Large areas of the replicated plasma membrane remain intact for observation. Colloidal gold probes are probably the only probes of sufficient density that can be detected on these surfaces. 

Iridium Black.204 Iridium(III) hydroxide is reduced in water at 90°C and 8 MPa H2 for 40 min, in the same way as in the preparation of osmium black. The iridium(III) hydroxide is prepared by adding an aqueous lithium hydroxide solution dropwise to an 1% aqueous solution of water-soluble iridium(III) chloride, IrCl3 3H20, at 90-95°C until the pH of the solution becomes 7.5-7.8 under stirring. By keeping the solution at the same temperature under stirring, the precipitate of iridium(III) hydroxide is separated out from its colloidal solution. The precipitate is collected, washed repeatedly with hot water, and then dried in vacuo. 

A characteristic property of the platinum metals consists in tin1 readiness with which they admit of being prepared in the colloidal stale as hydrosols. These latter possess powerful catalytic properties, and their accelerating influence upon the rate of decomposition of aqueous solutions of hydrogen peroxide has been carefully studied. The most, powerful catalyscr is colloidal osmium, followed in order of decreasing activity by platinum, palladium, and iridium.1... 

Osmium palladium platinum and ruthenium iridium rhodium.1 It is interesting to compare this order with that found for the activity of the colloidal metals in regard to the decomposition of hydrogen peroxide. The change in position of the osmium is remarkable. 

Osmium Hydrosol or Colloidal Osmium is readily prepared by reducing potassium osmate, K20s04, with hydrazine hydrate in the presence of some protective colloid such as gum acacia 2 or lysalbate (or protalbate) of sodium.3 The reduction may be effected with acrolein 4 if desired. 

Colloidal osmium may also be obtained by reduction of colloidal osmium dioxide. The last named is prepared (see p. 220) by reduction with hydrazine hydrate of potassium osmate solution suspended in lanolin, which serves as protective colloid. The product is dissolved in petroleum, precipitated with alcohol and reduced in a current of hydrogen at 50° to 60° C. A solution containing 21 per cent, of osmium has been obtained in this manner.5... 

Colloidal osmium readily undergoes oxidation it catalvtieally assists the oxidation of unsaturated compounds by gaseous hydrogen. In this respect it is stated to be even more effective than the finely divided metal, but less active than either platinum or iridium. Carbon monoxide combines with oxygen, yielding the dioxide, when shaken at ordinary temperatures with the hydrosol of osmium.7... 

Colloidal Osmium Dioxide.—It has already been mentioned that osmium dioxide, obtained either by reduction cf an alkali osmate with alcohol or by hydrolysis of an alkali chlorosmate, is precipitated in the colloidal form. 

A more permanent colloidal solution is obtained in the presence of a protective colloid. It may be prepared, for example,1 by impregnation of lanolin with a solution of potassium osmate. and subsequent reduction with hydrazine hydrate. The lanolin serves as the protective colloid. The product is dissolved in light petroleum and may be precipitated by addition of alcohol. By heating the precipitate to 50° C. in hydrogen, reduction to colloidal metallic osmium takes place. 

On the other hand, osmium tetroxide may be used to catalytically assist the reduction or hydrogenation of unsaturated oils like linseed or cotton-sced oils.2 The oil is mixed with a small quantity of the tetroxide, hydrogen passed through, and the whole warmed, just as when nickel or its oxides is used as catalyst (see p. 95). The osmium can be recovered, by treatment with charcoal, in the form of its dioxide, a colloidal solution of which is frequently formed in the oil by the reduction of the tetroxide during the process. 

When present in various compounds or alloys, osmium is conveniently estimated by ignition in a current of oxygen, collection in alcoholic alkali of the volatile tetroxide, and reduction with formaldehyde. The reduction product first forms a colloid, but is gradually precipitated and converted in metallic osmium by reduction in hydrogen at 230° to 250° C.3 Or the alcoholic solution may be treated with ammonium chloride and the precipitated osmyl diammine chloride reduced to metal in hydrogen. 

Occurronco and History of Osmium -Preparation -Properties Colloidal Osmium—Catalytic Activity—Atomic Weight—Uses Alloys. 

Colloidal dispersions of copper, palladium, silver, osmium, indium, platinum and gold can be prepared using both PVA and PVPD (Tkble 8). 

Concentration and temperature inversion of the catalytic properties of gold, platinum, osmium, and palladium chlorides at thermal and initiated polymerization of styrene and MMA has been discovered. The mechanism of ambiguous action of noble metal salts is caused by the competition of the initiating inOrence of monomer complexes with colloidal metal particles and the inhibition reaction proceeding by ligand transfer. 

Wohler obtained phosphorus by strongly heating a mixture of sand and bone-black (calcium phosphate and carbon) — the modern process, now carried out in the electric furnace. He prepared artificial nickel arsenide and worked on the separation of iridium and osmium in a pound of platinum residues given him by Dumas on a visit to Paris in 1833. A supposed silver suboxide, Ag40, prepared by Wohler by the action of caustic potash solution on a supposed subcitrate made by heating silver citrate in hydrogen at 100°, was not analysed and was probably a mixture of silver and silver oxide AggO the red colour of the solution of the subcitrate was probably due to colloidal silver. ... 

Another promising technique based on Raman spectroscopy is SERS. In this technique the molecules to be studied are adsorbed on gold or silver colloidal particles, leading to an impressive amplification of the signal (typically by a factor of 100-1000). This technique was recently employed by Leong and coworkers to localize the osmium complex 55 (Scheme 11.10) adsorbed on gold nanoparticles [152]. This time the amplified t/(CO) peaks of the complex have an intensity sufficient to allow study at concentrations in the micromolar range. 

The mechanism for this ostensibly homogeneous process, the Chalk-Harrod mechanism, [264] was based on classical organometallic synthetic and mechanistic research. Its foundation lies in the oxidative addition of the silane Si-H bond to the low oxidation state metal complex catalyst, a reaction which is well established in the organometallic literature. Lewis reported in 1986 that the catalyti-cally active solutions contained small (2.0 nm) platinum particles, and demonstrated that the most active catalyst in the system was in fact the colloidal metal. [60, 265] Subsequent studies established the relative order of catalytic activity for several precious metals to be platinum > rhodium > ruthenium = iridium > osmium. [266] In addition, a dependence of the rate on colloid particle morphology for a rhodium colloid was observed. [267]... 

Fig. 68. Type 5 Clara cell from a bronchiolus of a female white rat (breeder Winkehnann, Borchen-Kirchborchen), which received intramuscular injection of 150 mg DL-a-tocopherol acetate in a colloidal solution (Ephynal) per kg body weighty day, 5 days per week from April 12 to June 12, 1967 for a total of 40 days. Fixed on June 12, 1967 under methitural anaesthesia by intratracheal instillation of 2.5 % glutaraldehyde in phosphate buffer (pH 7.4) before opening the thorax. Postfixation with 1 % osmium tetroxide in phosphate buffer (pH 7.4). Contrasted en bloc for 12 h with 0.5 % uranyl acetate in 70 % ethanol. Embedded in a 2 8 mixture of methyl and butyl methacrylate. Sectioned at 50 nm. Lead citrate after Reynolds (1963). Plate 278/12...

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