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PubMed2002

Effects of fixatives on function of pulmonary surfactant.

The structure of pulmonary surfactant films remains ill defined. Although plausible film fragments have been imaged by electron microscopy, questions about the significance of the findings and even about the true fixability of surfactant films by the usual fixatives glutaraldehyde (GA), osmium tetroxide (OsO(4)), and uranyl acetate (UA) have not been settled. We exposed functioning natural surfactant films to fixatives within a captive bubble surfactometer and analyzed the effect of fixatives on surfactant function. The capacity of surfactant to reach near-zero minimum surface tension on film compression was barely impaired after exposure to GA or OsO(4). Although neither GA nor OsO(4) prevented the surfactant from forming a surface active film, GA increased the equilibrium surface tension to above 30 mN/m, and both GA and OsO(4) decreased film stability as seen in the slowly rising minimum surface tension from 1 to ~5 mN/m in 10 min. In contrast, the effect of UA seriously impaired surface activity in that both adsorption and minimum surface tension were substantially increased. In conclusion, the fixatives tested in this study are not suitable to fix, i.e., to solidify, surfactant films. Evidently, however, OsO(4) and UA may serve as staining agents.

Adsorption↗
PubMed1995

Granulation in amine-storage organelles of mouse megakaryocytes: X-ray microprobe analysis and radioautography.

The mechanisms and the processes of the storage of bivalent cations, ATP and 5-hydroxytryptamine (5HT) in the precursors of the amine-storage organelles of megakaryocytes were studied at the electron microscopic level. Although the precursors of the amine-storage organelles in the megakaryocytes fixed with glutaraldehyde and osmium tetroxide were empty, the electron opaque granules were observed in these organelles of the freeze-substituted megakaryocytes cut onto ethylene glycol. X-ray microprobe analysis demonstrated that they contained P, Mg and Ca. Quantitative differences in bivalent cations in the granules were not observed between megakaryocytes and blood platelets. Electron opaque uranaffin-reaction products were observed in the precursors of the amine-storage organelles of the megakaryocytes after treatment with the uranaffin reaction for ATP. However, few chromaffin positive granules were observed in the precursors of the amine-storage organelles after the chromaffin reaction for monoamines. Radioautographic analysis demonstrated that blood platelets avidly took up 3H-5HT but megakaryocytes were not able to accumulate 3H-5HT in vivo. These results indicate that megakaryocytes do not yet acquire the well developed uptake system of 5HT in vivo, while they readily accumulate cations and ATP in the precursors of the amine-storage organelles.

Adenosine Triphosphate↗
PubMed1983

The effect of osmium postfixation and uranyl and lead staining on the ultrastructure of young enamel in the rat incisor.

Enamel crystallites are electron opaque without osmium or heavy metal staining and give a crystalline electron diffraction pattern. Since the opacity and diffraction pattern are abolished from ultrathin sections of young enamel by floating on distilled water (Bishop and Warshawsky, 1982), the possibility that aqueous staining may also remove crystallites was tested. In addition, the effect of osmium postfixation on crystallite structure was examined. Rat incisors fixed by perfusion with a mixture of aldehydes were either nonosmicated or osmicated prior to dehydration. Incisor segments in the region of inner enamel secretion were embedded in the same Epon block to ensure reliable comparison. Osmicated enamel was more intensely stained with toluidine blue and more electron opaque than nonosmicated enamel. No other structural differences were seen. However, crystallites in osmicated enamel were more resistant to grid demineralization and electron beam damage. Routine staining was done by floating sections on solutions of uranyl acetate and lead citrate; sections were also floated on similar solutions from which the heavy metals were omitted. These solutions removed the electron opaque crystallites from the youngest enamel. Stained sections showed electron opaque crystallite-like structures similar to unstained enamel. When sections that were extracted by the solutions from which the metals were omitted were restained, they appeared identical to routinely stained enamel. It was concluded that staining of young enamel removes the crystallites and reveals only the organic matrix.

Aging↗
PubMed2002

Pairing of propellers: dimerization of octahedral ruthenium(II) and osmium(II) complexes of eilatin via pi-pi stacking featuring heterochiral recognition.

Five octahedral eilatin complexes of the type [M(L-L)(2)(eilatin)](2+) (M = Ru, Os; L-L = bipyridyl-type ligands) were synthesized, and their dimerization via pi-pi stacking was studied by crystallography and (1)H NMR techniques. The X-ray structures of these racemic complexes were solved and revealed that the eilatin complexes are organized as discrete dimers in which the eilatin residues of each complex are stacked in centrosymmetric packing. Chemical shift dependence on concentration in the (1)H NMR spectra support fast dimer-monomer equilibrium, and the structures of the dimers in acetonitrile solution are proposed to be analogous to their solid-state structures. Dimerization constants in acetonitrile were measured for the five racemic eilatin complexes that exhibit different structural parameters, as well as for the two enantiomeric forms of one of these complexes. They were found to be independent of the metal (Ru vs Os), strongly dependent on the steric effects introduced by the L-L ligands (2,2'-bipyridine, 1,10-phenanthroline, 2,9-dimethyl-1,10-phenanthroline, and 2,2'-biquinoline), and dependent on the optical purity of the complexes. A clear preference for heterochiral over homochiral dimer formation was demonstrated. This is the first report of chiral recognition in solution, exhibited by simple chemical systems held solely by pi-stacking interactions.

Alkaloids↗
PubMed2005

Detection of adsorption of Ru(II) and Os(II) polypyridyl complexes on gold and silver nanoparticles by single-photon counting emission measurements.

The present study describes a new application of ruthenium(II) tris(bipyridine) (Ru(bpy)3(2+)) and osmium(II) tris(bipyridine) (Os(bpy)3(2+)) as phosphorescent labels for the quantification of surface binding of molecules to gold and silver nanoparticles. The fraction of Ru(bpy)3(2+) and Os(bpy)3(2+) that is in solution can be distinguished from the surface-bound fraction by the relative lifetimes and integrated emission yields as determined by time-correlated single-photon counting (TCSPC) spectroscopy. Complementary steady-state measurements were carried out to confirm surface attachment of the phosphorescent label molecules. Although the emission of solutions of Ru(bpy)3(2+) and Os(bpy)3(2+) is quenched proportional to the concentration of 10 nm Au or 20 nm Ag nanoparticles, the quenching is static and not diffusional quenching observed in Stern-Volmer plots. The results demonstrate that time-resolved spectroscopy provides a rapid method for the measurement of surface binding of labeled molecules on metallic nanoparticles. While steady-state measurements require the preparation of a series of samples with varying quencher concentrations and a reference, the method described herein requires a single sample plus reference. The mechanism for phosphorescence quenching on Au and Ag nanoparticles is discussed in terms of energy and electron transfer theories.

Adsorption↗
PubMed1961

Preferential staining of nucleic acid-containing structures for electron microscopy.

Oriented fibres of extracted nucleohistone were employed as test material in a study of satisfactory fixation, embedding, and staining methods for structures containing a high proportion of nucleic acid. Fixation in buffered osmium tetroxide solution at pH 6, containing 10(-2)M Ca(++), and embedding in Araldite enabled sections of the fibres to be cut in which the orientation was well preserved. These could be strongly stained in 2 per cent aqueous uranyl acetate, and showed considerable fine structure. Certain regions in the nuclei of whole thymus tissue could also be strongly stained by the same procedure, and were identical with the regions stained by the Feulgen procedure in adjacent sections. Moreover, purified DNA was found to take up almost its own dry weight of uranyl acetate from 2 per cent aqueous solution. Strongest staining of whole tissue was obtained with very short fixation times-5 minutes or so at 0 degrees C. Particularly intense staining was obtained when such tissue stained in uranyl acetate was further stained with lead hydroxide. Although the patterns of staining by lead hydroxide alone and by uranyl acetate were similar in tissues fixed for longer times ((1/2) hour to 2 hours, at 0 degrees C or 20 degrees C), in briefly fixed material the DNA-containing regions appeared relatively unstained by lead hydroxide alone, whilst often there was appreciable staining of RNA-containing structures. Observations on the staining of some viruses by similar techniques are also described.

Coloring Agents↗
PubMed2006

Potential-, pH-, and isotope-dependence of proton-coupled electron transfer of an osmium aquo complex attached to an electrode.

An osmium complex, [OsII(bpy)2(4-aminomethylpyridine)(H2O)]2+, is attached to a mixed self-assembled monolayer on a gold electrode. The complex exhibits 1-electron, 1-proton redox chemistry (OsIII(OH)/OsII(H2O)) at pHs and potentials that are experimentally accessible with gold electrodes in aqueous electrolytes. The thermodynamic behavior and kinetic behavior of the system are investigated as a function of pH in both H2O and D2O. The two formal potentials and two pKa values are relatively constant for two chain lengths in H2O and in D2O. The standard rate constants at all pHs are strongly and uniformly affected by chain length, indicating that electronic coupling is the dominant factor controlling the rate of electron transfer. In both H2O and D2O, the standard rate constant is weakly dependent on the pH, exhibiting a minimum value midway between the pKa values. The kinetic isotope effect is small; standard rate constants decrease by roughly a factor of 2 in D2O over a wide range of pHs, but not at the more acidic pHs. The Tafel plots and plots of the transfer coefficient vs overpotential are asymmetrical at all pHs. These results are interpreted in terms of a larger reorganization energy for the OsII species and a smaller reorganization energy for the OsIII species. The OsIII reorganization energy is constant at all pHs in both H2O and D2O. The pH dependence of the OsII reorganization energy accounts for some or all of the pH dependence of the standard rate constant in H2O and D2O. The data deviate substantially from predictions of the stepwise proton-coupled electron-transfer mechanism. The observation of a kinetic isotope effect supports the concerted mechanism.

Electrochemistry↗
PubMed2006

Tuning the reactivity of osmium(II) and ruthenium(II) arene complexes under physiological conditions.

The Os(II) arene ethylenediamine (en) complexes [(eta(6)-biphenyl)Os(en)Cl][Z], Z = BPh(4) (4) and BF(4) (5), are inactive toward A2780 ovarian cancer cells despite 4 being isostructural with an active Ru(II) analogue, 4R. Hydrolysis of 5 occurred 40 times more slowly than 4R. The aqua adduct 5A has a low pK(a) (6.3) compared to that of [(eta(6)-biphenyl)Ru(en)(OH(2))](2+) (7.7) and is therefore largely in the hydroxo form at physiological pH. The rate and extent of reaction of 5 with 9-ethylguanine were also less than those of 4R. We replaced the neutral en ligand by anionic acetylacetonate (acac). The complexes [(eta(6)-arene)Os(acac)Cl], arene = biphenyl (6), benzene (7), and p-cymene (8), adopt piano-stool structures similar to those of the Ru(II) analogues and form weak dimers through intermolecular (arene)C-H...O(acac) H-bonds. Remarkably, these Os(II) acac complexes undergo rapid hydrolysis to produce not only the aqua adduct, [(eta(6)-arene)Os(acac)(OH(2))](+), but also the hydroxo-bridged dimer, [(eta(6)-arene)Os(mu(2)-OH)(3)Os(eta(6)-arene)](+). The pK(a) values for the aqua adducts 6A, 7A, and 8A (7.1, 7.3, and 7.6, respectively) are lower than that for [(eta(6)-p-cymene)Ru(acac)(OH(2))](+) (9.4). Complex 8A rapidly forms adducts with 9-ethylguanine and adenosine, but not with cytidine or thymidine. Despite their reactivity toward nucleobases, complexes 6-8 were inactive toward A549 lung cancer cells. This is attributable to rapid hydrolysis and formation of unreactive hydroxo-bridged dimers which, surprisingly, were the only species present in aqueous solution at biologically relevant concentrations. Hence, the choice of chelating ligand in Os(II) (and Ru(II)) arene complexes can have a dramatic effect on hydrolysis behavior and nucleobase binding and provides a means of tuning the reactivity and the potential for discovery of anticancer complexes.

Antineoplastic Agents↗
PubMed1992

Structural and histochemical studies of Golgi complex differentiation in salivary gland cells during Drosophila development.

Morphological alterations in the Golgi complex (GC) and changes in the distribution of acid phosphatase (AcPase), thiamine pyrophosphatase (TPPase), complex carbohydrates and reduced osmium tetroxide compounds in this organelle were studied in the salivary gland cells of Drosophila during larval and prepupal development. The morphology and the AcPase, TPPase and complex carbohydrates cytochemical patterns of the Golgi complex varied characteristically during cell differentiation. At the early 3rd instar period the Golgi complex consisted mainly of vesiculated cisternae, and AcPase activity was observed in all cisternae but not in the secretory granules. As development proceeded to the late 3rd instar the Golgi complex displayed its typical appearance, consisting of four to six cisternae, and only the two to three cisternae towards the trans-face as well as the trans-Golgi network and some of the immature secretory granules exhibited AcPase reactivity. In the course of a 'wave' of production of the 'glue' secretory granules proceeding proximally through the gland, the number of AcPase positive cisternae changed correspondingly. After secretion of the 'glue' secretory granules, the size of the Golgi complex decreased and almost all cisternae displayed AcPase reactivity. The detection of TPPase activity presented some specificity problems, since staining was observed not only in the GC cisternae but in the endoplasmic reticulum (ER) and microvilli. The reaction products were seen in a few GC vesicles during the early 3rd instar and in the trans side of the organelle at the end of the 3rd instar. During production of the secretory granules, every GC cisterna was intensely stained. These results agree with previous findings suggesting that AcPase and TPPase in secretory cells may be primarily involved in the processing of exportable proteins. The vicinal (vic)-glycol groups of the complex carbohydrates were detected using the periodic acid/thiocarbohydrazide/silver proteinate (PA-TCH-SP) technique. During synthesis of the 'glue' secretory granules, the reaction products were observed over the GC cisternae and the trans-Golgi network, with increasing intensity from the cis to the trans side of the organelle. No PA-TCH-SP staining was observed over the GC cisternae during the early 3rd instar. Following discharge of the 'glue' secretory granules, all GC cisternae displayed uniform PA-TCH-SP staining. After OsO4 impregnation, the reaction products were observed mainly in ER and mitochondria and rarely in the GC. In numerous cells, only the mitochondria were stained, while in many cases the ER of neighboring cells exhibited differential staining.(ABSTRACT TRUNCATED AT 400 WORDS)

Acid Phosphatase↗
PubMed2003

The remarkable reactivity of high oxidation state ruthenium and osmium polypyridyl complexes.

There is a remarkable redox chemistry of higher oxidation state M(IV)-M(VI) polypyridyl complexes of Ru and Os. They are accessible by proton loss and formation of oxo or nitrido ligands, examples being cis-[RuIV(bpy)2(py)(O)]2+ (RuIV=O2+, bpy=2,2'-bipyridine, and py=pyridine) and trans-[OsVI(tpy)(Cl)2(N)]+ (tpy=2,2':6',2' '-terpyridine). Metal-oxo or metal-nitrido multiple bonding stabilizes the higher oxidation states and greatly influences reactivity. O-atom transfer, hydride transfer, epoxidation, C-H insertion, and proton-coupled electron-transfer mechanisms have been identified in the oxidation of organics by RuIV=O2+. The Ru-O multiple bond inhibits electron transfer and promotes complex mechanisms. Both O atoms can be used for O-atom transfer by trans-[RuVI(tpy)(O)2(S)]2+ (S=CH3CN or H2O). Four-electron, four-proton oxidation of cis,cis-[(bpy)2(H2O)RuIII-O-RuIII(H2O)(bpy)2]4+ occurs to give cis,cis-[(bpy)2(O)RuV-O-RuV(O)(bpy)2]4+ which rapidly evolves O2. Oxidation of NH3 in trans-[OsII(tpy)(Cl)2(NH3)] gives trans-[OsVI(tpy)(Cl)2(N)]+ through a series of one-electron intermediates. It and related nitrido complexes undergo formal N- transfer analogous to O-atom transfer by RuIV=O2+. With secondary amines, the products are the hydrazido complexes, cis- and trans-[OsV(L3)(Cl)2(NNR2)]+ (L3=tpy or tpm and NR2-=morpholide, piperidide, or diethylamide). Reactions with aryl thiols and secondary phosphines give the analogous adducts cis- and trans-[OsIV(tpy)(Cl)2(NS(H)(C6H4Me))]+ and fac-[OsIV(Tp)(Cl)2(NP(H)(Et2))]. In dry CH3CN, all have an extensive multiple oxidation state chemistry based on couples from Os(VI/V) to Os(III/II). In acidic solution, the OsIV adducts are protonated, e.g., trans-[OsIV(tpy)(Cl)2(N(H)N(CH2)4O)]+, and undergo proton-coupled electron transfer to quinone to give OsV, e.g., trans-[OsV(tpy)(Cl)2(NN(CH2)4O)]+ and hydroquinone. These reactions occur with giant H/D kinetic isotope effects of up to 421 based on O-H, N-H, S-H, or P-H bonds. Reaction with azide ion has provided the first example of the terminal N4(2-) ligand in mer-[OsIV(bpy)(Cl)3(NalphaNbetaNgammaNdelta)]-. With CN-, the adduct mer-[OsIV(bpy)(Cl)3(NCN)]- has an extensive, reversible redox chemistry and undergoes NCN(2-) transfer to PPh3 and olefins. Coordination to Os also promotes ligand-based reactivity. The sulfoximido complex trans-[OsIV(tpy)(Cl)2(NS(O)-p-C6H4Me)] undergoes loss of O2 with added acid and O-atom transfer to trans-stilbene and PPh3. There is a reversible two-electron/two-proton, ligand-based acetonitrilo/imino couple in cis-[OsIV(tpy)(NCCH3)(Cl)(p-NSC6H4Me)]+. It undergoes reversible reactions with aldehydes and ketones to give the corresponding alcohols.

Ammonia↗
PubMed1997

Atomic force microscopy and cytochemistry of chromatin from marsupial spermatozoa with special reference to Sminthopsis crassicaudata.

Atomic force microscopy (AFM) of the nuclear topology of spermatozoa from two marsupial species, Smithopsis crassicaudata and Trichosurus vulpecula was investigated to determine the structural organisation of the chromatin subunits. That of the former species is of special interest as it has a peripheral nucleohistone region (C2) as well as a nuclease-resistant, nucleoprotamine core region (C1). Atomic force microscopy showed that the C2 region contained clusters of 120-160 nm nodules, whereas the C1 region exhibited smaller 50-80 nm nodules. The spermatozoa nuclei of Trichosurus, which has mainly nucleoprotamines, contained higher order chromatin structures of similar size to those from the C1 region of Sminthopsis. This study shows that nucleohistones and nucleoprotamines of marsupial sperm form distinct higher order conformations. For the second part of this work, the chromatin density and affinity for cationic stains of Sminthopsis spermatozoa were determined. Spermatozoa were observed with the transmission electron microscopy (TEM) either unstained or stained with metal salts. In the unstained specimens, the C2 nucleohistone region appeared more electron-lucent than the C1 region. When large cations such as uranyl were used, the reverse situation was observed. Therefore, the electron-dense appearance of the C2 chromatin in conventionally stained material may be due to the presence of net negative DNA charges that attract the cations used for EM staining, whereas the C1 chromatin may lack excess DNA negative charges that attract these stains and thus appears less electron-dense.

Animals↗
PubMedDate not supplied

'Wiring' of lactate oxidase within a low-redox potential electron-conducting hydrogel.

Lactate electrodes based on electron-conducting hydrogels made by cross-linking lactate oxidase and the redox polymer formed upon complexing polyvinyl imidazole with [Os(dmo-bpy)2Cl]+/2+ (dmo-bpy = 4,4'-dimethoxy-2,2'-bipyridine) on vitreous carbon electrode surfaces were investigated. The redox potential of the hydrogels was -69 mV, versus the standard calomel electrode (SCE), and their lactate electro-oxidation current reached a plateau at +50 mV (SCE). Urate and acetaminophen were not electro-oxidized at this potential at rates that would interfere with the lactate assays, but ascorbate was catalytically oxidized by the gel. At 6 mM lactate concentration, switching of the atmosphere from argon to O2, reduced the current by 40 percent, showing that the rate of electron transfer from the reduced enzyme to the gel was slow.

Cross-Linking Reagents↗
PubMed1995

DNA changes involved in the formation of metaphase chromosomes, as observed in mouse duodenal crypt cells stained by osmium-ammine. I. New structures arise during the S phase and condense at prophase into "chromomeres," which fuse at prometaphase into mitotic chromosomes.

BACKGROUND: In the hope of understanding how chromosomes condense at mitosis, we took advantage of a subdivision of the cell cycle into 11 stages to examine the changes in DNA taking place during the stages preceding the emergence of metaphase chromosomes. METHODS: To identify DNA changes, pieces of mouse duodenum were fixed in formaldehyde, and sections of the rapidly dividing cells of the crypts were stained by the osmium-ammine method, which is specific for the detection of DNA in the electron microscope. RESULTS: Throughout the cell cycle, DNA is present in nucleofilaments composed of rows of 11-nm-wide nucleosomes. At stage I, during which the DNA-synthesizing or S phase of the cell cycle begins, some of the nucleofilaments are compacted in the heterochromatin accumulations associated with nuclear envelope and nucleoli, while the others are scattered in the nucleoplasm where they appear either "free" or "attached" to the heterochromatin. This DNA distribution is similar to that observed in the noncycling cells examined. After the beginning of the S phase, "free" nucleofilaments are seen to assemble into structures composed of compacted nucleofilaments and referred to as "aggregates"; these make their appearance at stage II and increase in size through stage III up to the end of S during stage IV. Meanwhile, the heterochromatin associated with nuclear envelope and nucleoli expands toward the nucleoplasm in the form of protrusions referred to as "bulges," which gradually enlarge during stages III and IV, while the heterochromatin shrinks and eventually vanishes. On average, a total of 1,171 aggregates and bulges are formed in the nucleus during the S phase. At the apparition of stage V, which corresponds approximately to prophase, aggregates and bulges are rapidly gathered into an average of 288 spheroidal bodies referred to as "chromomeres." These are connected to one another by nucleofilamentous bridges in such a way as to be lined up in rows. The formation of rows of chromomeres represents in the electron microscope the prophasic condensation observed in the light microscope. Finally, during stage VIa, which corresponds to prometaphase, the chromomeres approach one another within each row, make contact, and coalesce to become the 40 chromosomes of the mouse, which during stage VIb are organized in the equatorial plate of metaphase. CONCLUSIONS: The condensation of metaphase chromosomes occurs in three main steps. The first and longest takes place during the S phase, as nucleofilaments are assembled into aggregates, while the heterochromatin gives rise to bulges. The brief second step occurs toward the beginning of prophase, when the numerous aggregates and bulges are congregated into a limited number of chromomeres, which are lined up in rows. The third step takes place during the brief prometaphase, when the chromomeres of a row coalesce into a mitotic chromosome.

Animals↗
PubMed1995

DNA changes involved in the formation of metaphase chromosomes, as observed in mouse duodenal crypt cells stained by osmium-ammine. II. Tracing nascent DNA by bromodeoxyuridine into structures arising during the S phase.

BACKGROUND: Since it has been found that new chromatin structures make their appearance in the nucleus during the DNA-synthesizing or S phase of the cell cycle, the question arises as to how these structures are related to the nascent DNA. METHODS: DNA-containing structures were detected in sections of mouse duodenal crypt cells by the DNA-specific osmium-ammine procedure. In the same sections, the nascent or newly-replicated DNA was localized during stages I-IV of the cell cycle (corresponding to four successive parts of the S phase) by immunogold labeling of the DNA precursor bromodeoxyuridine (BrdU) in mice sacrificed 10 min after its injection. Moreover, the fate of the nascent DNA with time was traced up to 6 hr after the injection. (The nomenclature of the DNA-containing structures is that proposed by El-Alfy et al., 1995.) RESULTS: Ten minutes after BrdU injection, the gold particles indicative of nascent DNA are associated with discrete nucleofilaments scattered in the nucleoplasm, but not with the compacted nucleofilaments making up the heterochromatin or the new S phase structures named "aggregates." The gold-particle-associated discrete nucleofilaments are classified into three types: a) The "free" nucleofilaments have been given this name, since they appear to be independent of heterochromatin and aggregates; nearly all gold particles are over these at stage I; but the numbers of particles over them decreases from stage I to IV. b) The "aggregate-attached" nucleofilaments project from the surface of the aggregates; the number of particles over these is high at stages II and III but decreases at stage IV. c) The "heterochromatin-attached" nucleofilaments project from the surface of the heterochromatin; the number of particles over these increases from stage II to IV. By 1 hr after BrdU injection, gold particles can be over loose clumps of nucleofilaments at stages I and II, but are mostly over small aggregates at stage II, midsized aggregates and small heterochromatin-associated "bulges" at stage III and large aggregates and large bulges at stage IV. By 2-6 hr, virtually all particles are over aggregates and bulges, frequently deep within them. CONCLUSIONS: The distribution of the gold particles at 10 min reveals that DNA is synthesized in discrete nucleofilaments that are "free" or "aggregate-attached" or "heterochromatin-attached." In contrast, by one and especially two hours, the gold particles are present over aggregates and bulges, indicating that, after discrete nucleofilaments acquire nascent DNA, they are displaced to become part of these structures. More precisely, the aggregates arise from the repeated addition of replicated portions of "free" nucleofilaments, while the bulges arise from the repeated addition of replicated portions, of "heterochromatin-attached" nucleofilaments. Aggregates and bulges are the two initial building stones from which mitotic chromosomes are eventually formed.

Animals↗
PubMed2005

An Os(II)--bisbipyridine--4-picolinic acid complex mediates the biocatalytic growth of au nanoparticles: optical detection of glucose and acetylcholine esterase inhibition.

The complex Os(II)-bisbipyridine-4-picolinic acid, [Os(bpy)(2)PyCO(2)H](2+) (1), mediates the biocatalyzed growth of Au nanoparticles, Au NPs, and enables the spectroscopic assay of biocatalyzed transformations and enzyme inhibition by following the Au NP plasmon absorbance. In one system, [Os(bpy)(2)PyCO(2)H](2+) mediates the biocatalyzed oxidation of glucose and the growth of Au NPs in the presence of glucose oxidase, GOx, AuCl(4) (-), citrate and Au NP seeds. The mechanism of the Au NPs growth involves the oxidation of the [Os(bpy)(2)PyCO(2)H](2+) complex by AuCl(4) (-) to form [Os(bpy)(2)PyCO(2)H](3+) and Au(I). The [Os(bpy)(2)PyCO(2)H](3+) complex mediates the GOx biocatalyzed oxidation of glucose and the regeneration of the mediator 1. Citrate reduces Au(I) and enlarges the Au seeds by the catalytic deposition of gold on the Au NP seeds. In the second system, the enzyme acetylcholine esterase, AChE, is assayed by the catalytic growth of the Au NPs. The hydrolysis of acetylcholine (2) by AChE to choline is followed by the [Os(bpy)(2)PyCO(2)H](3+) mediated oxidation of choline to betaine and the concomitant growth of the Au NPs. The mediated growth of the Au NPs is inhibited by 1,5-bis(4-allyldimethylammonium-phenyl)pentane-3-one dibromide (3). A competitive inhibition process was demonstrated (K(M)=0.13 mM, K(I)=2.6 microM) by following the growth of the Au NPs.

2,2'-Dipyridyl↗
PubMed1993

Ultrastructural localization of DNA in leukemic cells using osmium ammine B.

In order to determine whether there were any differences in distribution of nuclear DNA between acute lymphocytic leukemia (ALL) and acute myelogenous leukemia (AML), the localization of DNA in blasts from the bone marrow or buffy coat of 30 patients with ALL and 30 patients with AML was examined ultrastructurally by staining with osmium ammine B. By the ultrastructural cytochemistry, DNA in ALL cells was clumped in the nuclei, while in AML cells, it was dispersed. DNA had accumulated around the nucleoli of some blasts, and flecks of DNA were observed in nucleoli of a majority of blasts. The perinucleolar and intranucleolar DNA distribution could be classified into four types. The types with abundant perinucleolar DNA were frequently observed in ALL blasts, while the majority of AML blasts showed scant perinucleolar DNA. The types with intranucleolar flecks of DNA were more prominent in leukemic cells than in normal immature leukocytes. In conclusion, the pattern of distribution of DNA in the nuclei of leukemic cells differs between ALL and AML.

Adolescent↗