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At least 19 recordsLinked to original sources
PubMed1984

The use of osmium-thiocarbohydrazide-osmium (OTO) and ferrocyanide-reduced osmium methods to enhance membrane contrast and preservation in cultured cells.

The preservation and contrast of membranous structures in cultured cells using various postfixation procedures prior to embedding have been investigated. These include routine OsO4, ferrocyanide-reduced OsO4, osmium-thiocarbohydrazide-osmium (OTO), and ferrocyanide-reduced osmium-thiocarbohydrazide-ferrocyanide-reduced osmium (R-OTO). With standard ethanol-Epon dehydration/embedding techniques, a dramatic improvement in both membrane contrast and preservation of bilayer membrane structure was achieved using preembedding OTO in cultured cells. R-OTO yielded similar enhanced preservation and contrast of membranes. Both of these methods also resulted in an increase in the contrast of diaminobenzidine reaction product from horseradish peroxidase activity, and of lipid droplets and lipoprotein particles. However, R-OTO did not cause the same increase in the density of proteinaceous elements as was seen with the OTO method. Ferrocyanide-reduced osmium alone showed significant advantages for quantitation of immunocytochemistry using ferritin labels with bismuth subnitrate counterstain. These methods should have general usefulness for the preservation of lipid-containing structures in cultured cells.

3,3'-Diaminobenzidine↗
PubMed1997

Synthesis of Bis(aliphatic amine)osmium(II), Bis(arylamido)osmium(IV), and Bis(imido)- and Oxo(imido)osmium(VI) Porphyrins.

The syntheses, characterization, and reactivity of a series of osmium porphyrins, Os(II)(Por)(H(2)NR)(2) [Por = dianions of octaethylporphyrinato (OEP), tetraphenylporphyrinato (TPP), meso-tetrakis(p-tolyl)porphyrinato (TTP), meso-tetrakis(4-chlorophenyl)porphyrinato (4-Cl-TPP), meso-tetrakis(3,4,5-trimethoxyphenyl)porphyrinato (3,4,5-MeO-TPP), R = (t)Bu; Por = TPP, R = (i)Pr], Os(II)(Por)(HNEt(2))(2) (Por = TPP, 3,4,5-MeO-TPP), Os(IV)(Por)(NHAr)(2) (Por = OEP, TPP, 3,4,5-MeO-TPP; Ar = Ph, 4-F-Ph), Os(VI)(Por)(N(t)Bu)(2) (Por = TPP, TTP, 4-Cl-TPP, 3,4,5-MeO-TPP), Os(VI)O(Por)(N(t)Bu) (Por = TPP, TTP, 4-Cl-TPP, 3,4,5-MeO-TPP), and Os(VI)O(Por)(4-F-PhN) (Por = TPP, 3,4,5-MeO-TPP) are described. The complexes Os(Por)(HNAr)(2) are prepared from the reactions of Os(Por)(N(2))(THF) with arylamines in aerobic tetrahydrofuran. Air oxidations of Os(Por)(H(2)N(t)Bu)(2) in tetrahydrofuran and in the presence of H(2)N(t)Bu give OsO(Por)(N(t)Bu) and Os(Por)(N(t)Bu)(2). The X-ray crystal structures of OsO(TTP)(N(t)Bu).EtOH and Os(4-Cl-TPP)(N(t)Bu)(2) have been determined. Crystal data for OsO(TTP)(N(t)Bu).EtOH: monoclinic, space group P2(1)/c, a = 13.546(6) Å, b = 23.180(3) Å, c = 16.817(3) Å, beta = 90.84(2) degrees, V = 5279.7(1.0) Å(3), Z = 4. Os(4-Cl-TPP)(N(t)Bu)(2): monoclinic, space group P2(1)/c, a = 11.046(2) Å, b = 18.380(3) Å, c = 23.640(4) Å, beta = 97.22(1) degrees, V = 4759.8(1.0) Å(3), Z = 4. The Os=O and Os=N(t)Bu distances in OsO(TTP)(N(t)Bu).EtOH are 1.772(7) and 1.759(9) Å, respectively. The Os=N(t)Bu distances in Os(4-Cl-TPP)(N(t)Bu)(2) average 1.775 Å. The imido angles range from 165.8(8) to 170.6(9) degrees. For the infrared spectra of these complexes, a discussion on the "oxidation state marker" band in the vicinity of 1000 cm(-)(1) is presented. The differences in the electronic properties of osmium porphyrins at various oxidation states are also described.

Journal Article↗
PubMed1967

Coordination polymers of osmium: the nature of osmium black.

The design of cytochemical reagents that yield osmiophilic products from which an osmium black may be derived on exposure to osmium tetroxide has resulted in new methods described previously for the ultrastructural demonstration of enzyme activity and functional groups of macromolecules with the electron microscope. Attempts to determine the nature of the osmium black end products have been frustrated by their insolubility. The preparation of watersoluble analogs and their characterization as polymers suggest that the insoluble osmium blacks are coordination polymers. This is consonant with the unusually favorable properties of osmium black in electron microscopy. Although polymers of osmium have frequently been postulated as the end products of reaction of osmium tetroxide with tissue conistituents or with other organic compounds, this is the first example of their characterization.

Glycols↗
PubMed1994

Osmium conductive metal coating for SEM specimen using sublimated osmium tetroxide in negative glow phase of DC glow discharge.

A new method of osmium conductive metal coating for scanning electron microscopy specimens using osmium tetroxide in direct current glow discharge and its apparatus have been devised. Anode and cathode plates are placed in a gas reactor, sublimated osmium tetroxide is introduced, and glow discharge is generated. As a result, the gas between the electrodes instantaneously becomes plasma. At the specimen surface, which is placed in the negative glow phase on the cathode plate, positively ionized osmium molecules are directly adhered and deposited, thereby leaving a completely amorphous metal coating of osmium. As a result, the formed coating precisely matched the fine structure of the specimen surface, and even when irradiated with a strong electron beam was free of heat damage, electrification and contamination. The secondary electron emission efficiency of the coating was also good. Furthermore, no granularity of the film surface was observed even when viewed at a high magnification. In this way, a superior osmium conductive metal coating was obtained.

Erythrocytes↗
PubMed1981

Enhanced visualization of peripheral nerve and sensory receptors in the scanning electron microscope using cryofracture and osmium-thiocarbohydrazide-osmium impregnation.

Two methods of specimen preparation for the scanning electron microscope (SEM) have been combined for the reliable exposure and examination of nervous system tissue. When the specimen is postfixed with OSO4 prior to aqueous cryofracturing, large internal surfaces of nervous tissue are exposed, with minimal distortion to the cytoarchitecture. All tissue surfaces and interstices are subsequently impregnated with a conductive, metallic layer of osmium using a modified osmium-thiocarbohydrazide-osmium technique (OTOTO). This OTOTO technique permits SEM examination without any additional vacuum evaporated or ion-sputtered metallic layers, and has been found to eliminate specimen charging reliably. Nervous tissue has been examined in the secondary electron mode of the SEM with unrestricted use of beam currents varying from 1.3 to 60 microamperemeter, at accelerating voltages ranging from 2.5 to 80 kV, and at both low (10 X) and high (80 000 X) magnifications. In addition, a differential deposition of osmium in the tissue after the OTOTO technique has been identified using both transmission electron microscopy and energy dispersive X-ray microanalysis. The enhanced mass-density of myelin resulting from the amplification of osmium's natural affinity for unsaturated lipids was best demonstrated by the backscatter electron mode of the SEM. This mode of imaging was found useful in the identification of myelin sheaths.

Animals↗
PubMed1996

One-Pot Synthesis of Dihalo(porphyrinato)osmium(IV) Complexes. Evidence for Monohalo(carbonyl)osmium(III) Intermediates.

trans-Dichloro-, trans-dibromo-, and trans-diiodoosmium(IV) tetraarylporphyrins were obtained by extremely facile synthetic routes directly from the reactions of the corresponding (carbonyl)osmium(II) complexes with CCl(4), CBr(4), and CI(4), respectively. At short reaction times, appreciable amounts of intermediates-one for each reaction-were observed by spectroscopic investigations. These intermediates were shown to be (carbonyl)(halo)(porphyrinato)osmium(III) complexes by independent preparation of an authentic (carbonyl)(bromo)(porphyrinato)osmium(III) complex, which was identical to the reaction intermediate in the reaction of CBr(4) and very similar to those of the other reactions. This provided strong evidence for the reaction mechanism, two stepwise one-electron oxidations of the metal ion. The relatively strong binding of carbon monoxide to osmium(III) is proposed to be an important factor in avoiding dimerization of the reaction intermediates.

Journal Article↗
PubMed1999

Osmium(VI) Nitrido and Osmium(IV) Phosphoraniminato Complexes Containing Schiff Base Ligands.

A series of osmium(VI) nitrido complexes containing Schiff base ligands, [Os(VI)(N)(L)Cl] (L = salophen or salen), have been synthesized by reaction of the ligand with [NBu(n)(4)][Os(VI)(N)Cl(4)] in the presence of 2,6-dimethylpyridine. The nu(Os&tbd1;N) for the salophen complexes occur at around 1070 cm(-)(1) and are insensitive to the nature of the substituents present on the Schiff base ligand. The structures of [Os(N)(salophen)(MeOH)]ClO(4) and [Os(N)(5,5-Cl(2)salophen)(MeOH)]ClO(4) have been determined by X-ray crystallography, and the Os&tbd1;N bond distances are 1.651 and 1.66 Å, respectively. The osmium(VI) nitrido complexes react rapidly with triphenylphosphine to produce the corresponding osmium(IV) phosphoraniminato complexes, [Os(IV)(NPPh(3))(L)Cl]. The osmium(IV) complexes exhibit reversible Os(V/IV) and Os(IV/III) couples in cyclic voltammetry. The E(1/2) values show linear correlations with the Hammett constants sigma(p) of the substituents on the Schiff base ligand. The structure of [Os(IV)(NPPh(3))(salophen)Cl] has been determined by X-ray crystallography. The rather long Os-N(P) bond length (1.92 Å) and acute Os-N-P bond angle (149.6 degrees ) suggest that there is no significant multiple-bond character in the Os-N bond. The kinetics of nitrogen atom transfer from a series of 5,5'-disubstituted salophen nitrido complexes to PPh(3) have been studied in CH(3)CN at 25.0 degrees C by stopped-flow spectrophotometric method. The following rate law was obtained: -d[Os(VI)]/dt = k(2)[Os(VI)][PPh(3)]. The reactivities of the complexes were found to follow a Hammett correlation of log(k(X)/k(H)) with sigma(p), with a rho value of 1.9 +/- 0.1. The positive rho value is consistent with a transition state involving electrophilic attack by the nitrido ligand on the phosphorus atom.

Journal Article↗
PubMed2002

Evidence of an equilibrium between selenides and osmium(VIII) reagents and selenoxides and osmium(VI) reagents.

Driving the equilibrium between selenides and osmium(VIII) reagents with selenoxides and osmium(VI) by a subsequent reaction (rearrangement of allyl selenoxides to allyl alcohols or addition of osmium(VIII) species on C=C double bonds) to one side, allows the transformation of methyl geranyl selenides to linalool and of methyl citronellyl selenoxide to 6,7-dihydroxy citronellyl selenide.

Journal Article↗
PubMed1988

Scanning electron microscopy of skin surface and the internal structure of corneocyte in normal human skin. An application of the osmium-dimethyl sulfoxide-osmium method.

A horny layer of normal human skin prepared according to the newly developed osmium-dimethyl sulfoxide-osmium method was examined using scanning electron microscopy. On the skin surface, cytomembranes of the uppermost corneocytes frequently had unilateral, very slightly flat-elevated, zonal areas along the junctions between the corneocytes. The uppermost corneocytes peeled off along the junctions, leaving the remnants of their cell bodies in the junctional areas. In the cracked surface, cytomembranes of the corneocytes protruded from the plane of their cytoplasmic surface. In the lateral junction between the corneocytes, the cytomembranes of the corneocytes were in tight contact with each other, while occasionally the marginal bands had become detached from the cytomembranes. In the vertical connection, cleavages formed between the cytomembranes of the corneocytes. There were thick woollen thread-like structures about 10-30 nm thick in the cytoplasm of the corneocytes. They formed fine irregular meshworks, with their tips projecting digitally: Transmission electron microscopy revealed these structures as most likely being keratin bundles transformed during processing.

Cell Membrane↗
PubMed1976

Tissue fixation and osmium black formation with nonvolatile octavalent osmium compounds.

Several compounds of osmiumVIII, including potassium osmiamate and coordination complexes of OsO4 with ammonia and various heterocyclic nitrogen compounds, have been synthesized and characterized. They have also been evaluated as substitutes for OsO4 in postfixation of biological specimens and in light and electron microscopic cytochemical methods resulting in osmium black formation. The most useful of these osmic compounds, a molecular addition complex of hexamethylenetetramine (methenamine) with OsO4, has a negligible vapor pressure of OsO4. It has the molecular formula C6H12N4.2OsO4 and has been designated osmeth. Although it has only limited solubility, aqueous solutions of the compound (or of OsO4) can be rapidly prepared by dissolution in a minimal amount of dimethylformamide and subsequent dilution with distilled water or buffer. Although stable in the solid state, the complex in solution undergoes partial dissociation releasing OsO4, and the odor of OsO4 becomes apparent. Such solutions of osmeth are (approximately 0.25%) considerably less concentrated with respect to OsO4 than solutions (1-2%) ordinarily employed for ultrastructural preservation or in cytochemical studies. Osmeth has limited value for postosmication after glutaraldehyde fixation because the generation (release) of OsO4 appears to be slow. Adequate osmication of tissue blocks exists only at the surface, but effective osmication can be achieved throughout tissue sections. In cytochemical reactions resulting in the formation of osmium blacks, the osmeth solutions are as effective as OsO4 solutions of equivalent concentrations. Our findings indicate that OsO4 solutions of less than 1% may be satisfactorily utilized in many cytochemical studies. Osmeth is safer and more convenient to handle than OsO4 because small amounts may be solubilized as needed. It should be considered as a substitute for OsO4 in ultrastructural cytochemistry. These results suggest that the effectiveness of OsO4 as a fixative may, in part, be related to its nonpolarity. The infrared spectra indicate that the OsO4 molecule is tetrahedral, perfectly symmetrical and, therefore, as a whole nonpolar. As a consequence, it could be expected to readily penetrate charged surfaces of tissues, cells, and organelles. The spectral studies show that osmeth is much less symmetrical and, to that extent, polar; thus, it penetrates biomembranes less readily.

Animals↗
PubMed1977

Osmium-labeled polynucleotides. The reaction of osmium tetroxide with deoxyribonucleic acid and synthetic polynucleotides in the presence of tertiary nitrogen donor ligands.

Osmium tetroxide in the presence of pyridine or 2,2'-bipyridine has been found to react completely with the pyrimidine moieties (thymine, uracil, and cytosine) in polynucleotides. Pyrimidine osmate ester moieties, L2OSO4-pyrimidine, were formed. The OSO4 has added across the 5,6 double bond and L=pyridine or 1/2-bipyridine. The pyridine derivatives were not stable and decomposed slowly after the OSO4-pyridine reagent was removed by gel chromatography. Labeled poly(uridylic acid) lost osmium completely during gel chromatography unless the eluent contained a high concentration of pyridine. The products formed between OSO4-bipyridine and polynucleotides were much more stable and the OS label was retained during and after gel chromatography. Both the OSO4-pyridine and OSO4-bipyridine reagents reacted more rapidly than the OSO4-CN-reagent.

Binding Sites↗
PubMed1988

Ultrastructural discrimination of lipid droplets and vesicles in atherosclerosis: value of osmium-thiocarbohydrazide-osmium and tannic acid-paraphenylenediamine techniques.

Electron microscopy of atherosclerotic arterial tissue commonly fails to distinguish lipid vesicles from droplets, especially when these are found in the extracellular space. The distinction is important, because vesicular or membranous lipid is composed of phospholipid and unesterified cholesterol, whereas neutral lipid in droplet form implies the presence of cholesteryl ester in atherosclerosis. A new procedure with sequential tannic acid and p-phenylenediamine treatments of osmicated tissue (TA-PDA) allows reliable ultrastructural discrimination of lipid vesicles and droplets. The multilamellar character of many vesicles is revealed. Extracellular droplets are found to possess many surface pits associated with membranous blebs. Pitting of droplets is especially evident after the use of an alternative tissue processing technique, the osmium-thiocarbohydrazide-osmium (OTO) sequence applied en bloc. The two complementary techniques will prove useful for electron microscopic studies of atherosclerotic and other lipid-rich tissues.

Adult↗
PubMed1978

Osmium-labeled polynucleotides: reaction of osmium tetraoxide, with poly-1,N6-ethenoadenylic acid.

Osmium tetraoxide, in the presence of ligands such as pyridine and bipyridine, adds across the etheno bridge of 1,N6-etheno-9-methyladenine and poly-1,N6-ethenoadenylic acid. The Os:P ratio in the labeled polynucleotide was approximately equal to 1 when bipyridine was used as the stabilizing ligand. A similar study with polycytidylic acid, which had been partially modified with chloroacetaldehyde so that some bases were converted to 3,N4-ethenocytosine, gave an OS:P ratio of approximately equal to 1.3. Calf-thymus DNA, in which the adenine and cytosine bases were modified by chloroacetaldehyde, gave an Os:P ratio of approximately equal to 1 after 24 h. These results suggest that 3,N4-ethenocytosine will add two Os labels.

Adenosine Triphosphate↗