Osmium tetroxide technique

The electron micrographs of the various ERL-4221-CTBN systems were prepared with the osmium tetroxide technique (3). The castings were stained by reaction with osmium tetroxide vapors for 24 hours. Ultrathin specimens, approximately 1000 A thick, were cut with the Reichert OMU2, ultramicrotome equipped with a diamond knife and were stained again for one hour. The osmium tetroxide selectivity stained the rubber phase, while the epoxy remained unaffected, revealing many structural features in the polyphase systems with excellent contrast and... 

Figure 4. Electron-micrograph of grafted latex ABS polymer by the osmium tetroxide technique...

The sample was prepared by osmium tetroxide technique (magnification, 8670 X), dark phase = rubber particles, white spots in the particles are occluded polystyrene... 

The sample was prepared by osmium tetroxide technique (magnification, 4130 X)... 

Condie, A., Ecles, R., Bprresen, A.-L., Coles, C., Cooper, C., and Prosser, J. (1993) Detection of point mutations in the p53 gene comparison of single-strand conformation polymorphism, constant denaturant gel electrophoresis, and hydroxylamine and osmium tetroxide techniques. Human Mutat. 2, 58-66. 

To produce contrast between phase domain for electron microscopy the osmium tetroxide technique of Kato (1 18) was employed. Samples were exposed to OsO. vapor for one week, during which time they darkened. The samples were cut... 

The Smith technique consisted of fixing the smear in osmium tetroxide vapor, immersion in HCI, mordanting in dilute formaldehyde, and staining with aqueous basic fuchsin. The method was said to possess certain advantages over the procedure of Robinow. 

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. 

The distortions induced in the DNA double helix by the interstrand cross-links have been characterized by several techniques. As judged by chemical probes (diethyl pyrocarbonate, hydroxylamine, osmium tetroxide), antibodies to cisplatin-modified poly(dG-dC)-poly(dG-dC), natural (DNase I) and artificial (1,10-phenanthroline-copper complex) nucleases, the cytosine residues are accessible to the solvent, and the distortions are located at the level of the adduct [48-50]. From the electrophoretic mobility of the multimers of double-stranded oligonucleotides containing a single interstrand cross-link [50] it is deduced that the DNA double helix is unwound (79°) and its axis is bent (45°). 

The first heterogeneous osmium catalyst applicable for asymmetric dihydroxylation reactions was described by Kobayashi and coworkers (Table 9, entry 1) [38, 39]. Osmium tetroxide was enveloped in a polymer capsule by microencapsulation techniques [40,41]. The asymmetric dihydroxylation of transmethylstyrene with poly(acrylonitrile-co-butadiene-co-styrene) microencapsulated (ABS-MC) osmium tetroxide as catalyst, NMO as the cooxidant, and (DHQD)2PHAL as the chiral ligand completed in 88% yield with 94% ee [38]. The catalyst and the chiral ligand were reused in five consecutive runs without loss of activity. However, the use of NMO as cooxidant required the slow... 

Other electron-micrographs were prepared according to Kato s technique (27). Osmium tetroxide made the rubber particles dark and distinct. The thickness of the ultrathin specimen was 1000 A. 

The technique was demonstrated with gap junctions of connexin43-tetracysteine that had been pulse chased with FlAsH and ReAsH [11] as described above in Section 8.1.4.2.1. Fixation of the cells and strong illumination of ReAsH in the presence of DAB and 02 gave localized deposition of precipitates that could be stained with osmium tetroxide. Electron microscopy revealed electron dense material only at cell regions that had been stained with ReAsH (Fig. 8.1-5). Higher magnification of cross sections of gap junction plaques showed structures with appropriate dimensions of individual connexons. Photoconverted vesicles of characteristic size trafficking to or from the plaque could also be visualized. 

Several methods of studies have been developed. Osmium-staining technique, pioneered by Kato [1967], is one of the most successful methods for observing crazing in rubber toughened plastics. It depends upon a reaction between osmium tetroxide, OsO, and double bonds in PBD and other unsaturated polymers. However, it is not suitable for saturated rubbers. 

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