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PubMed2003

Spectroscopic and computational investigations of stable radical anions of triosmium benzoheterocycle clusters.

The variable temperature (1)H and (13)C NMR and EPR spectra of the stable radical anions [Os(3)(CO)(9)(micro(3)-eta(2)-L)(micro-H)] (LH=phenanthridine, 1; 5,6-benzoquinoline, 2), and [Os(3)(CO)(10)(micro(3)-eta(2)-L)(micro-H)] (LH=quinoxaline, 3) are reported. The radical anions 1(-), 2(-), and 3(-) can be prepared by both exhaustive electrolysis and partially by chemical reduction with cobaltocene and with sodium dispersion (only with sodium dispersion in the case of 3(-)). DFT calculations on 1-3 reveal that the LUMO for the electron-deficient compounds 1 and 2 involves significant contributions from both the heterocyclic ligand and the two metal atoms bridged by the ligand and the micro-hydride. The character of this orbital rationalizes the previously observed regioselective reactions of these complexes with nucleophiles. In contrast, the LUMO for the electron precise 3 involves only ligand-based orbitals. Partial chemical reduction of 1 and 2 requires an excess of either cobaltocene or sodium, and their (1)H and (13)C NMR spectra reveal selective line broadening of those proton resonances that are predicted by DFT calculations to bear the greatest amount of free spin density. The variable temperature behavior of the partially chemically reduced species of 1 and 2 indicates that electron transfer between the reduced/unreduced cluster pair and between the cobaltocene/cobaltocenium pair occurs on the NMR timescale. The radical anions of 1 and 2 prepared by exhaustive electrolysis show an EPR signal at room temperature, while the NMR signals are uniformly broadened. Compound 3 appears to be partially reduced by sodium at room temperature and shows uniformly broadened (1)H NMR resonances at room temperature that sharpen significantly at -80 degrees C. The temperature dependence of the spectra are discussed in terms of the effects of relative electron nuclear relaxation processes, chemical exchange, and the results of the DFT calculations.

Anions↗
PubMed1989

Potential bile acid metabolites. 14. Hyocholic and muricholic acid stereoisomers.

The complete set of the eight theoretically possible stereoisomeric 3,6,7-trihydroxy-5 beta-cholanic acids, four of which are new, related to hyocholic and muricholic acids were prepared from chenodeoxycholic acid. The principal reactions used were 1) cis-dihydroxylation of delta 6-compounds with osmium tetroxide/N-methylmorpholine N-oxide; 2) trans-dihydroxylation of 6 alpha, 7 alpha-epoxy compounds with boron trifluoride etherate in N,N-dimethyl-formamide; 3) inversion of equatorial 3 alpha-hydroxylated compounds to the corresponding 3 beta-epimers with diethyl azodicarboxylate/triphenylphosphine/formic acid; and 4) stereoselective reduction of 7-keto derivatives with zinc borohydride (or sodium borohydride) and by metallic potassium/tert-amyl alcohol.

Bile Acids and Salts↗
PubMed1975

Glycogen, its chemistry and morphological appearance in the electron microscope.11. The complex formed in the selective contrast staining of glycogen.

Selective contrast staining of glycogen in untreated ultrathin sections of aldehyde-fixed tissues, double-fixed with 1% osmium tetroxide containing 0.05 M K3Fe(CN)6 as reported previously (De Bruijn, 1973), may also be obtained by the addition of either K4Fe(CN)6,K3Co(CN)6,K2Ru(CN)6, or K4Os(CN)6. On the other hand, addition of K3Cr(CN)6, K2Ni(CN)4, K3Mn(CN)6, K3Rh(CN)6, K2Pd(CN)4, K2Pt(CN)4, or K3Ir(CN)6 produces no effect. Hexavalent osmium oxide compounds, such as K2OsO4 and OsO3-2 pyridine, react selectively with a native (or acquired) ligand in the aldehyde-fixed glycogen, but do not render it more electron dense than its immediate surroundings. The presence of these osmium oxides is detected and they are rendered more electron dense by an accumulation reaction by the application on ultrathin sections of phosphotungstic acid (PTA) or a mixture of K2OsO4 and K4Fe(CN)6. As selective contrast staining of glycogen is also obtained by double fixation of the aldehyde-fixed tissue with 0.05 M K2OsO4 solutions containing 0.05 M K4Fe(CN)6 or 0.05 M K4Os(CN)6, it is postulated that in such tissue, both the selective reaction of K2OsO4 with the ligand in the aldehyde-fixed glycogen, and the accumulation of heavy metal at the sites occupied by the K2OsO4, occur simultaneously. A proposal for the constitution of this heavy metal osmium/cyanide complex is formulated and arguments are presented that both compounds are formed in the selective contrast stained glycogen areas of such treated tissues. The relative contribution of the components to the final contrast and its complex character is demonstrated by staining ultrathin glutaraldehyde sections intermittently with 0.05 M solutions of K2OsO4 and K4Fe(CN)6; it is shown that after at least three intermittent reactions with both K2OsO4 and K4Fe(CN)6, the glycogen areas in such sections became contrast stained.

Animals↗
PubMed2006

Conformationally gated photoinduced processes within photosensitizer-acceptor dyads based on osmium(II) complexes with triarylpyridinio-functionalized terpyridyl ligands: insights from experimental study.

[(ttpy)Os(tpy-ph-TPH(3)(+))](3+) (2), [(ttpy)Os(tpy-xy-TPH(3)(+))](3+) (3), [(ttpy)Os(tpy-ph-TPH(2)(NO(2))(+))](3+) (4), and [(ttpy)Os(tpy-xy-TPH(2)(NO(2))(+))](3+) (5) are a series of dyads made of an Os(II) bis-tpy complex (tpy = 2,2':6',2"-terpyridine) as the photosensitizer (P) and 2,4,6-triarylpyridinium group (TP(+)) as the electron acceptor (A). These dyads were designed to form charge-separated states (CSS) upon light excitation. Together with analogous Ru(II) complexes (7-10), they have been synthesized and fully characterized. We describe herein how intramolecular photoinduced processes are affected when the electron-accepting strength of A (by nitro-derivatization of TP(+)) and/or the steric hindrance about intercomponent linkage (by replacing a phenyl spacer by a xylyl one) are changed. Electronic absorption and electrochemical behavior revealed that (i) chemical substitution of TP(+) (i.e., TP(+)-NO(2)) has no sizable influence on P-centered electronic features, (ii) reduction processes located on TP(+) depend on the intercomponent tilt angle. Concerning excited-state properties, photophysical investigation evidenced that phosphorescence of P is actually quenched in dyads 4 and 5 only. Ultrafast transient absorption (TA) experiments allowed attributing the quenching in conformationally locked dyad 5 to oxidative electron transfer (ET) from the (3)MLCT level to the TP(+)-NO(2) acceptor (k(el) = 1.1 x 10(9) s(-)(1)). For 4, geometrically unlocked, the (3)MLCT state was shown to first rapidly equilibrate (reversible energy transfer; k(eq) approximately 2 x 10(9) s(-)(1)) with a ligand centered triplet state before undergoing CSS formation. Thus, the pivotal role of conformation in driving excited-state decay pathways is demonstrated. Also, inner P structural planarization as a relaxation mode of the (3)MLCT states has been inferred from TA experiments.

Electrons↗
PubMed1992

The activity of metal compounds against aerobic and anaerobic bacteria.

We evaluated the antimicrobial activity of two metal compounds, JM-1397 (OsO2[xylyl]2) and JM-2469 (AuCl[S2CPEt3]). Both inhibited methicillin-susceptible and methicillin-resistant Staphylococcus aureus at concentrations of 0.5-2 micrograms/ml, with a minimum inhibitory concentration (MIC90) of 1 microgram/ml for JM-1397 and 0.5 microgram/ml for JM-2469. Similar concentrations inhibited methicillin-susceptible and -resistant coagulase-negative staphylococci (S. epidermidis, S. haemolyticus, and S. saprophyticus). JM-2469 inhibited group A, B, C, F, and G beta-hemolytic streptococci and viridans group streptococci at 1-8 micrograms/ml (MIC90 4 micrograms/ml) but Enterococcus faecalis and E. faecium had MICs of 8-16 micrograms/ml. JM-1397 had MICs for these organisms of greater than 64 micrograms/ml. Bacteroides fragilis, other Bacteroides, and Clostridium species were inhibited by less than or equal to 0.12-4 micrograms/ml (MIC90, 0.5 microgram/ml). MICs of both compounds for Enterobacteriaceae and Pseudomonas spp. were greater than 64 micrograms/ml. These studies show that osmium and gold compounds have potential as topical agents against Gram-positive and anaerobic species.

Anti-Bacterial Agents↗
PubMed2006

Conformationally gated photoinduced processes within photosensitizer-acceptor dyads based on osmium(II) complexes with triarylpyridinio-functionalized terpyridyl ligands: insights from theoretical analysis.

A theoretical analysis, based on density functional theory, has been carried out to study photoinduced processes within a recently experimentally characterized (Lainé, P. P.; Bedioui, F.; Loiseau, F.; Chiorboli, C.; Campagna, S. J. Am. Chem. Soc. 2006, http://dx.doi.org/10.1021/ja058357w.) series of Os(II) bis-tpy complexes (tpy = 2,2':6'2' '-terpyridine) functionalized by 2,4,6-triarylpyridinium groups, TP+. These dyad systems, designed to produce a charge-separated state (CSS) upon light excitation, are made up of a photosensitizer unit (P, the metal complex) and a tunable acceptor unit (A, the TP+). A full ab initio characterization of the electronic and structural properties of the lowest-lying triplet excited states, as well as of the CSS, allowed for a complete rationalization of the photoinduced processes taking place within the dyads. Among salient insights, theory allowed (i) substantiation of the inner P structural planarization as the relaxation mode of the MLCT states, (ii) confirmation of the existence of a ligand-centered triplet excited state (3LC) shown to essentially involve the nitro substituent of A (TP+-NO2) and lying very close in energy to the P-centered 3MLCT state, and (iii) a demonstration that the energy of the 3LC level is independent of intercomponent tilt angle (theta1). On this basis, the occurrence of a reversible electronic energy transfer between the 3MLCT and the 3LC states could be substantiated and shown to depend on the intramolecular conformation represented by theta1, which actually governs their electronic coupling (essentially via the degree of intercomponent conjugation). These computational issues were checked against experimental data already available and the results of a specifically undertaken photophysical study. Finally, CSS formation has been confirmed by studying the spin density patterns of reduced nitro-derivatized dyads. Taken together, these findings accurately account for the different excited-state behaviors of the dyads as a function of the level of structural restriction of their intercomponent conformation (and related amplitude for torsional fluctuations), thus providing theoretical evidence of conformationally gated photoinduced electron- and energy-transfer processes.

Fluorometry↗
PubMed2006

Optical sensing of parts per million levels of water in organic solvents using redox-active osmium chromophore-based monolayers.

Optical sensing of parts per million (ppm)-levels of H2O (10-300 ppm) in an organic solvent with robust, osmium chromophore-based monolayers is demonstrated. The H2O-induced reduction of the covalently bound osmium(III) complex is fully reversible and can be readily monitored by UV/vis absorption spectroscopy. The thermally robust sensor can be reactivated chemically within 3 min.

Furans↗
PubMed2006

Stabilization of NH tautomers of quinolines by osmium and ruthenium.

Complexes OsH2Cl2(PiPr3)2 and RuH2Cl2(PiPr3)2 promote the tautomerization of quinoline and 8-methylquinoline to NH tautomers, which lie about 44 kcal.mol-1 above the usual CH tautomers. The NH tautomers are stabilized by coordination to the metal center and by means of a Cl...HN interaction. As a consequence, the six-coordinate elongated dihydrogen complexes OsCl2{kappa-C2-(HNC9H5R)}(eta2-H2)(PiPr3)2, the five-coordinate derivatives RuCl2{kappa-C2-(HNC9H5R)}(PiPr3)2, and the six-coordinate dihydrogen compounds RuCl2{kappa-C2-(HNC9H5R)}(eta2-H2)(PiPr3)2 (R = H, Me) have been isolated and characterized.

Organometallic Compounds↗
PubMed1995

Artefacts in electron microscopy: ultrastructural features of chrysiasis.

Eleven cases of chrysiasis have been studied ultrastructurally and by electron probe microanalysis. Tissue samples were examined both with and without osmium and uranyl acetate staining. There was a significant morphological difference in the appearance of the gold deposits within aurosomes between the two groups. The untreated group showed finely granular deposits, often arranged in a linear fashion. Aurosomes from samples treated with osmium and uranyl acetate showed more electron-dense deposits and star-like formations. We propose that treatment of the tissue with osmium and uranyl acetate causes a change in the electron microscopic appearance of aurosomes, including the formation of the characteristic star-like aurosomes.

Antirheumatic Agents↗
PubMed1992

Alternative staining methods for Lowicryl sections.

A number of stains and stain combinations have been identified that, when used with the hydrophilic resin Lowicryl K11M, produce marked improvements over aqueous uranyl and lead salts (UA-Pb) in terms of low granularity, specificity, and range of components contrasted. Three test specimens, tobacco mosaic virus (TMV), starfish sperm, and cultured mouse fibroblasts, were used to evaluate stain characteristics. UA-Pb showed a preference for nuclei acids, which were stained specifically by osmium ammine-B at pH 1.5. A number of stain combinations in which UA was followed or preceded by salts containing barium, manganese, tungsten, molybdenum, and vanadium provided excellent staining of protein-containing components, each stain combination being unique in terms of the degree to which specific components were discriminated. These stains were particularly effective for visualizing internal components of the nucleus where a number of fibrillar and particulate structures not seen with UA-Pb were well contrasted.

Acrylic Resins↗
PubMed2007

Ultrafast and ultraslow oxygen atom transfer reactions between late metal centers.

Oxotrimesityliridium(V), (mes)3Ir=O (mes = 2,4,6-trimethylphenyl), and trimesityliridium(III), (mes)3Ir, undergo extremely rapid degenerate intermetal oxygen atom transfer at room temperature. At low temperatures, the two complexes conproportionate to form (mes)3Ir-O-Ir(mes)3, the 2,6-dimethylphenyl analogue of which has been characterized crystallographically. Variable-temperature NMR measurements of the rate of dissociation of the mu-oxo dimer combined with measurements of the conproportionation equilibrium by low-temperature optical spectroscopy indicate that oxygen atom exchange between iridium(V) and iridium(III) occurs with a rate constant, extrapolated to 20 degrees C, of 5 x 107 M-1 s-1. The oxotris(imido)osmium(VIII) complex (ArN)3Os=O (Ar = 2,6-diisopropylphenyl) also undergoes degenerate intermetal atom transfer to its deoxy partner, (ArN)3Os. However, despite the fact that its metal-oxygen bond strength and reactivity toward triphenylphosphine are nearly identical to those of (mes)3Ir=O, the osmium complex (ArN)3Os=O transfers its oxygen atom 12 orders of magnitude more slowly to (ArN)3Os than (mes)3Ir=O does to (mes)3Ir (kOsOs = 1.8 x 10-5 M-1 s-1 at 20 degrees C). Iridium-osmium cross-exchange takes place at an intermediate rate, in quantitative agreement with a Marcus-type cross relation. The enormous difference between the iridium-iridium and osmium-osmium exchange rates can be rationalized by an analogue of the inner-sphere reorganization energy. Both Ir(III) and Ir(V) are pyramidal and can form pyramidal iridium(IV) with little energetic cost in an orbitally allowed linear approach. Conversely, pyramidalization of the planar tris(imido)osmium(VI) fragment requires placing a pair of electrons in an antibonding orbital. The unique propensity of (mes)3Ir=O to undergo intermetal oxygen atom transfer allows it to serve as an activator of dioxygen in cocatalyzed oxidations, for example, acting with osmium tetroxide to catalyze the aerobic dihydroxylation of monosubstituted olefins and selective oxidation of allyl and benzyl alcohols.

Cold Temperature↗
PubMed1982

Perfusion fixation of lungs for structure-function analysis: credits and limitations.

The quality of tissue preservation in lungs fixed by vascular perfusion has been reevaluated. Excised rabbit lungs inflated to 60% of total lung capacity were perfused (zone III conditions) with different but widely used fixatives. The effects of the perfusates on pertinent physiological variables have been assessed by a continuous monitoring, the effects on the pulmonary microstructure by qualitative and morphometric analysis of electron micrographs. Important results include the following. 1) Perfusions with isotonic glutaraldehyde at flow rates within the physiological range produce large increases of perfusion pressure and lung weight that reflect intracellular, interstitial, and intra-alveolar edema. 2) No edema occurs if glutaraldehyde is added to isotonic buffer solutions (total osmolarity 510 mosM). 3) Glutaraldehyde as sole perfusate does not fully eliminate the retractive force of lung tissue. Upon release of transpulmonary pressure the lungs retract by an indeterminable amount. 4) Satisfactory results can be obtained by sequential perfusion with osmium tetroxide and uranyl acetate or glutaraldehyde (510 mosM) followed by osmium tetroxide and uranyl acetate. The latter combination yields optimal preparations to study the alveolar and capillary architecture but causes a hyperosmotic volume loss of lung cells (cell shrinkage).

Animals↗
PubMed2000

Electrochemical characterization and DNA-binding property of dipyridophenazine complexes of osmium (II).

Novel dipyridophenazine (DPPZ) complexes of osmium (II), [Os(L)2(DPPZ)]2+ [L = 2,2'-bipyridyl (bpy)(1), 4,4'-diamino-2,2'-bipyridyl (DA-bpy)(2), 4,4'-dimethyl-2,2'-bipyridyl(DM-bpy)(3), and 4,4'-dicarboxyl-2,2'-bipyridyl (DC-bpy)(4)] have been synthesized and characterized. The DNA-binding properties of the complexes were studied by electrochemical methods. As the results, complex 2 shows higher affinity to DNA than other osmium complexes. The binding constant, K of complex 2 to calf thymus DNA has been determined to be 2.3 x 10(7) M-1 by normal pulse voltammetry (NPV).

Animals↗