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At least 1,423 records · Page 79Linked to original sources
PubMed2004

Paclitaxel production by plant-cell-culture technology.

Plant cells catalyze multiple-step reactions of secondary metabolite biosynthesis, and selectively synthesize chiral compounds with polycyclic structures. Taking advantage of this characteristic, we studied the production of the anticancer drug paclitaxel, which is currently produced in limited supply. Callus culture investigations indicate that woody plant medium supplemented with 10(-5) mol L(-1) 1-naphthylacetic acid and without the NH4+ -type ion is the best condition for growth of the callus. The accumulation of paclitaxel and related taxanes in Taxus plants is thought to be a biological response to specific external stimuli. Several signal transducers were screened; taxane biosynthesis was strongly promoted by methyl jasmonate (MeJA) and silver thiosulfate (STS) as an anti-ethylene compound. Of ten taxane-type diterpenoids isolated from T. baccata suspension-cultured cells treated with MeJA, five have a phenylisoserine side-chain at the C-13 position of the taxane skeleton. Time-course analysis revealed two regulatory steps in taxane biosynthesis: the taxane-ring formation step and the acylation step of the C-13 position. Methyl jasmonate promoted the formation of the taxane-ring. The production of paclitaxel reached a maximum level of 295 mg L(-1) in a large-scale culture of T. x media cells using a two-stage process.

Antineoplastic Agents↗
PubMed1998

The acidophilic nature of neuronal Golgi impregnation.

The mechanisms of Golgi impregnation of neurons has remained enigmatic for decades. Recently, it was suggested that divalent (di)chromate anions play a role in the Golgi impregnation process. Therefore, we incubated slices of (para)formaldehyde-fixed rat brain tissue in solutions of potassium (di)chromate, phosphate, chloride or nitrate at pH 6 or 7. Slices were then immersed in solutions of silver nitrate and processed for light microscopical analysis. At pH 6, dichromate probes resulted in dense and homogeneous impregnation of neuronal cytoplasm (typical impregnation). At pH 7, chromate probes showed solely partial cytoplasmic and heavy nuclear-region neuron impregnation (atypical impregnation). Phosphate probes at pH 6 resulted in typical impregnation, whereas at pH 7 phosphate probes gave atypical impregnation. Both at pH 6 and 7, chloride and nitrate probes did not yield any Golgi impregnation. These findings confirmed the pH-dependence of silver-chromate Golgi impregnation as well as the correctness of corresponding acidic silver-phosphate impregnation. Our study revealed a previously unknown, strong anion-dependence of Golgi impregnation, suggesting that hydrogenated monovalent anions are carriers of the neuron impregnation.

Animals↗
PubMed1986

Chemical spill exposure assessment.

POSSM, the PCB On-Site Spill Model, is a contaminant transport model developed to predict environmental concentrations associated with a chemical spill. The model predicts daily changes in chemical concentrations on a spill site (e.g., in soil and on vegetation) and losses of chemical due to volatilization, surface runoff/soil erosion, and leaching to groundwater. Spill areas consisting of soil/vegetation and/or an impervious surface (e.g., asphalt and concrete) can be analyzed, as can different spill cleanup practices. POSSM is used to analyze exposure levels associated with a hypothetical capacitor spill. While the model was developed for PCB spills, it is generally applicable to a number of organic compounds.

Accidents↗
PubMed1981

Localization of 3H-thymidine in oocyte Mitochondria from Schistosoma mansoni.

Cytoplasmic 3H-thymidine incorporated in oocytes of Schistosoma mansoni as seen on light microscope autoradiograms was removed by DNAase but not RNAase. On electron microscope autoradiograms, silver grains produced by 3H-thymidine were closely associated with mitochondria of oocytes. High resolution autoradiograms of 3H-actinomycin D, a compound which binds to nuclear and mitochondrial DNA, showed a majority of extranuclear silver grains was associated with mitochondria of oocytes. Exposure of worm sections to 4', 6-diamidino-2-phenylindole (DAPI), a compound that forms a fluorescent complex with DNA, produced a brilliant fluorescence in nuclei and cytoplasm of oocytes which was removed by DNAase but not RNAase. Incorporation of 3H-thymidine into nuclei and cytoplasmic components of oocytes was inhibited by two DNA-binding compounds, DAPI and acriflavin. This evidence indicted that the thymidine label emanated from mitochondrial DNA within the closely packed mitochondria of mature oocytes of S. mansoni.

Acriflavine↗
PubMed2001

Voltammetric behavior of L-cysteine in the presence of CPB at a silver electrode.

The voltammetric behavior of L-cysteine at a silver electrode is described. L-Cysteine can be anodically accumulated at a silver electrode surface as a sparingly soluble silver salt; at more negative potentials, the insoluble compound is stripped cathodically yielding a small current peak at about -1.10 V (vs. SCE). In the presence of cetyl pyridine bromide (CPB), the stripping peak shifts slightly to a more negative potential, and the peak height increases significantly. Thus, the peak becomes more useful for the determination of L-cysteine. In contrast to other surfactants, CPB can improve the accumulation and stripping of L-cysteine obviously. The voltammetric behavior of cysteamine, 3-mercaptopropionic acid and homocysteine is discussed as well.

3-Mercaptopropionic Acid↗
PubMed2000

Gold toning preserves integrity of silver enhanced immunogold particles during osmium tetroxide treatment for demonstration of a biogenic amine.

We describe a protocol that enhances immunolabelling of nervous tissue for ultrastructural study. Insect tissue is fixed, sectioned, and labelled with a polyclonal antiserum against serotonin and a secondary antibody conjugated with 1 nm colloidal gold. The gold particles are silver-enhanced to ease detection and then protected by gold toning. Finally, the tissue is post fixed in glutaraldehyde fixative followed by osmium tetroxide and further processed for electron microscopy. We demonstrated on insect nervous tissue that gold toning protects marker particles from the influence of osmium tetroxide. Use of buffered solutions throughout the protocol led to well preserved ultrastructural details, and marker particle size was not reduced with a short gold toning time. We also suggest use of this protocol for vertebrate or other invertebrate tissue.

Animals↗
PubMed1982

Suppression of the argyrophil III reaction by mercapto compounds (a prerequisite for the intensification of certain histochemical reactions by physical developers).

The tissue structure catalyse the interaction of silver ions with reducing molecules dissolved in physical developers, producing metallic silver grains bound at the sites of their formation (argyrophil III reaction). This reaction can be considerably slowed by a treatment with thioglycolic acid or certain other mercapto compounds before development. This observation offers a means for intensifying the end-products of certain histochemical reactions through the use of physical developers, without the microscopic image being interfered with or masked by the "unspecific" staining originating from the argyrophil III reaction.

Brain↗
PubMed1995

Trapidil inhibits endothelial cell proliferation and angiogenesis in the chick chorioallantoic membrane and in the rat cornea.

The effects of trapidil, a coronaro-active drug which has been shown to inhibit the mitogenic activity of platelet derived growth factor (PDGF), have been investigated on the proliferation of the human endothelial cells (HUV-EC-C), on the neovascularization in the chorioallantoic membrane of the chick embryo (CAM) as well as on the angiogenesis of rat cornea following chemical injury. The proliferation of HUV-EC-C in the presence of trapidil (25 and 250 micrograms/mL) was significantly inhibited by 19 and 25% respectively, compared to controls. On 2-days old CAMs, agarose disks containing 100-150 micrograms of trapidil produced an avascular zone indicating significant antiangiogenic activity, while control agarose disks were without effect. Corneal neovascularization was induced by applying a silver nitrate/potassium nitrate applicator to the rat eyes. A 6-day-treatment with eye drops of a solution of 10 mg/mL trapidil significantly decreased the rate of vessel growth compared with vehicle controls. The antiangiogenic activity of trapidil was markedly increased by the association with hydrocortisone (1.34 mg/mL). These results suggest that trapidil, alone or in combination with a steroid, could be a promising candidate for the therapy of corneal diseases in which alterations induced by neovascular growth play a substantial role.

Allantois↗
PubMed2006

Silver staining method for DNA in polyacrylamide gels using eriochrome black T as a silver-ion sensitizer.

A sensitive silver staining method using eriochrome black T as a silver-ion sensitizer for DNA detection in polyacrylamide gels was developed. The sensitivity of this staining method was significantly improved by the new silver-ion sensitizer containing a diazo group, which has reducing power. The staining method lasted a total of approximately 15 min following a fixing step for 2 x 20 min. The detection limit of this staining method was 1-4 pg for PhiX174 DNA/HaeIII in both nondenaturing and denaturing polyacrylamide gels. This staining method was especially effective in low-base pair DNA, with a sensitivity that was approximately ten-fold higher than previously published silver staining methods.

Acrylic Resins↗
PubMed2006

Diel mercury-concentration variations in streams affected by mining and geothermal discharge.

Diel variations of concentrations of unfiltered and filtered total Hg and filtered methyl Hg were documented during 24-h sampling episodes in water from Silver Creek, which drains a historical gold-mining district near Helena, Montana, and the Madison River, which drains the geothermal system of Yellowstone National Park. The concentrations of filtered methyl Hg had relatively large diel variations (increases of 68 and 93% from morning minima) in both streams. Unfiltered and filtered (0.1-microm filtration) total Hg in Silver Creek had diel concentration increases of 24% and 7%, respectively. In the Madison River, concentrations of unfiltered and filtered total Hg did not change during the sampling period. The concentration variation of unfiltered total Hg in Silver Creek followed the diel variation in suspended-particle concentration. The concentration variation of filtered total and methyl Hg followed the solar photocycle, with highest concentrations during the early afternoon and evening and lowest concentrations during the morning. None of the diel Hg variations correlated with diel variation in streamflow or major ion concentrations. The diel variation in filtered total Hg could have been produced by adsorption-desorption of Hg2+ or by reduction of Hg(II) to Hg0 and subsequent evasion of Hg0. The diel variation in filtered methyl Hg could have been produced by sunlight- and temperature-dependent methylation. This study is the first to examine diel Hg cycling in streams, and its results reinforce previous conclusions that diel trace-element cycling in streams is widespread but often not recognized and that parts of the biogeochemical Hg cycle respond quickly to the daily photocycle.

Environmental Monitoring↗
PubMed2004

Interaction of phospholipid dispersions with water-soluble porphyrins as monitored by their Raman temperature profiles.

Raman scattering spectra of 1,2-dipalmitoyl-sn-glycero-3-phospho-rac-(1-glycerol) (DPPG) and 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) dispersions, mixed with water-soluble porphyrins, i.e. cationic copper(II)-5,10,15,12-tetrakis(4-N-methylpyridyl) and anionic silver(II)-5,10,15,20-tetrakis(4-carboxyphenyl)porphyrins, were measured in the 2800-3100 cm(-1) C-H stretching vibration region as a function of the temperature within the 5-55 degrees C range. Temperature profiles of Raman data were constructed from a quantitative data treatment based on factor analysis. This method is shown to be more efficient than the commonly used approach employing peak intensity ratios. Parameters of the gel phase to liquid crystal phase transition determined from Raman temperature profiles were used to monitor the porphyrin influence on DPPG and DPPC structures. Both negatively and positively charged porphyrins significantly perturb DPPC and DPPG dispersions, causing significant downshift of the transition temperature and broadening of the transition region. Water-soluble porphyrins are assumed to set at the outside part of phospholipid dispersions and interact via coulombic forces with charged lipid heads. For the cationic CuTMPyP, the strongest effect has been observed for negatively charged DPPG. In contrast, anionic AgTPPC4 has been found to interact more efficiently with DPPC possessing both positive and negative charges.

1,2-Dipalmitoylphosphatidylcholine↗
PubMed1995

Primer for bonding resin to metal.

OBJECTIVES: The purpose was to examine the effect on the bond strength and durability of a resin bond to metal of modification of a primer consisting of thiophosphoric methacrylate with phosphoric methacrylates and/or benzoyl peroxide. METHODS: Acrylic rods were bonded with a luting resin consisting of poly(methyl methacrylate) powder and a mixture of methyl methacrylate and tributylborane initiator to silver-palladium alloy (Ag-Pd), gold-silver alloy (Au-Ag), cobalt-chromium alloy (Co-Cr), and titanium (Ti) surfaces treated with various primers. The bonded samples were thermocycled for 2,000 cycles and the mean bond strengths were compared using one-way ANOVA and Duncan's new multiple range test at p < 0.05. RESULTS: Using primers of thiophosphoric methacrylate or phosphoric methacrylates alone, the bond strengths of Ag-Pd decreased significantly (p < 0.05) after thermocycling. The durability was significantly improved (p < 0.05) when thiophosphoric methocrylate was used in combination with the phosphate monomers. The additional use of benzoyl peroxide and heat treatment resulted in a significant increase (p < 0.05) in the durability of two groups; the mean bond strengths over 20 MPa and the lowest values remained unchanged even after 2,000 thermocycles. SIGNIFICANCE: The highest level of bond strength and durability to dental noble metals was achieved using a mixture of thiophosphoric and phosphoric methacrylates and benzoyl peroxide. These bond strength results are comparable to values obtained for base metals.

Acetone↗
PubMed1977

Surface properties of dental amalgam: roughness produced by setting reaction.

During the setting of dental amalgam, silver-mercury (gamma1) and tin mercury (gamma2) intermetallic compounds (phases) are formed. Since these compounds have distinct crystalline forms, they may be discerned on the surface of a setting sample. Visual identification of these phases on polished and etched samples is often difficult and, hence, surface morphology studies have an advantage in following the stages of the setting reaction. The purpose of this investigation was to use high-resolution light microscopy to follow the course of the setting reaction. Amalgam specimens were triturated and condensed against glass plates under pressure. The sample surfaces were then photographed under a high-resolution metallographic microscope using oblique illumination. The roughness of four samples for each alloy type was determined with a surface profile analyzer at times between ten minutes and 23 hours after trituration. An electron microprobe was used to identify the gamma1 and gamma2 phases. The gamma1 phase had a polyhedramorphology, and the gamma2 crystals formed intermeshed smooth areas. During the setting reaction, the average times for the roughness to reach 95% of the final value were 189, 227, 96, 65, and 116 minutes after trituration for the various amalgam types studied. All alloys tested required polishing several hours after trituration.

Crystallography↗
PubMed1999

Synthesis and Structural Characterization of Neutral Silver(I) Complexes with Arenephosphinothiols. Crystal Structures of [Ag(4){2-(Ph(2)P)-6-(Me(3)Si)C(6)H(6)S}(4)] and [Ag(4){2-(Ph(2)PO)-6-(Me(3)Si)C(6)H(3)S}(4)].

Silver complexes of the anionic forms of 2-(diphenylphosphino)benzenethiol [2-(Ph(2)P)C(6)H(4)SH] (1), 2-(diphenylphosphino)-6-(trimethylsilyl)benzenethiol [2-(Ph(2)P)-6-(Me(3)Si)C(6)H(3)SH] (2), and 2-(diphenylphosphinyl)-6-(trimethylsilyl)benzenethiol [2-(Ph(2)PO)-6-(Me(3)Si)C(6)H(3)SH] (3) have been prepared by an electrochemical procedure and characterized by spectroscopic (IR, (1)H, (13)C, and (31)P NMR) methods, and ligand 3 and [Ag(4){2-(Ph(2)P)-6-(Me(3)Si)C(6)H(3)S}(4)] (5) and [Ag(4){2-(Ph(2)PO)-6-(Me(3)Si)C(6)H(3)S}(4)] (6) complexes were characterized by X-ray crystallographic techniques. Crystal data for 3: C(21)H(23)OPSSi, monoclinic, P2(1)/n, a = 11.3730(4) Å, b = 11.1562(4) Å, c = 17.1153(6) Å, beta = 103.961(1) degrees, V = 2107.4(1) Å(3), Z = 4, 2730 reflections with I(o) > 2sigma(I(o)), R = 0.0621. Crystal data for 5: C(84)H(88)Ag(4)P(4)S(4)Si(4), tetragonal, P4(2)2(1)2, a = 18.8454(7) Å, b = 18.8454(7) Å, c = 24.596(2) Å, V = 8735.1(7) Å(3), Z = 4, 4676 reflections with I(o) > 2sigma(I(o)), R = 0.0286. Crystal data for 6: C(90)H(97)Ag(4)N(3)O(4)P(4)S(4)Si(4), trigonal, P1, a = 13.4567(1) Å, b = 14.4148(2) Å, c = 14.8080(2) Å, alpha = 99.130(1) degrees, beta = 98.815(1) degrees, g = 114.211(1) degrees, V = 2509.38(5) Å(3), Z = 1, 6345 reflections with I(o) > 2sigma(I(o)), R = 0.0505. The [Ag(4){2-(Ph(2)P)-6-(Me(3)Si)C(6)H(3)S}(4)] (5) compound is tetranuclear with an array of four silver atoms bridged by four sulfur atoms. Each silver atom has a distorted trigonal [AgS(2)P] environment with each ligand acting as P,S bidentate S-bridging ligand. The [Ag(4)(2-(Ph(2)PO)-6-(Me(3)Si)C(6)H(3)S}(4)] (6) complex is also tetranuclear, but in this case two of the silver atoms are [AgO(2)S(2)] tetracoordinated and the other two Ag atoms are [AgS(2)] two coordinated.

Journal Article↗
PubMed2006

Hydroxy- and mercaptopyridine pincer platinum and palladium complexes generated by silver-free halide abstraction.

A silver-free route has been employed for the synthesis of a number of Pd and Pt complexes supported by an NCN "pincer" ligand (NCN = [2,6-(Me2NCH2)2C6H3]-) via halide abstraction. This was achieved by the use of o-, m-, and p-hydroxypyridines or o- and p-mercaptopyridines in basic ethanol solutions. The acidic OH or SH protons are removed to generate the formally anionic ligands. X-ray crystal structure determination of these complexes shows that the bonding of the substituted pyridine ligands occurs exclusively through the pyridine N for hydroxypyridines and exclusively through the thiol S in mercaptopyridines. In the hydroxypyridine case, the ortho and para isomers tautomerize to generate pyridone structures with a covalent M-N bond, whereas the m-hydroxypyridine complex, which is unable to tautomerize, is found to still be bound through the pyridine N but in a zwitterionic structure. The mercaptopyridine complexes are the first reported examples of pincer-ligated Pd and Pt thiolate species. The pyridine ligands can be quantitatively exchanged for chloride by reaction with excess NH4Cl, a potentially useful chemical switch for ligation/decomplexation of this ligand type.

Chemistry, Inorganic↗
PubMed2004

Antagonists of human CCR5 receptor containing 4-(pyrazolyl)piperidine side chains. Part 2: Discovery of potent, selective, and orally bioavailable compounds.

Modifications of the alkyl acetic acid portion and the phenyl on pyrrolidine in our lead pyrazole compound 1 afforded the isopropyl compound 9. This compound is a potent CCR5 antagonist showing good in vitro antiviral activity against HIV-1, an excellent selectivity profile, and good oral bioavailability in three animal species. During this investigation, a new method for the preparation of alpha-(pyrrolidin-1-yl)-alpha,alpha-dialkyl acetic acid from a pyrrolidine and alpha-bromo-alpha,alpha-dialkyl acetic acid using silver triflate was discovered. This allowed us to prepare compounds such as 24 and 25 for the first time. A novel Pd-mediated N-dealkylation of alpha-(pyrrolidin-1-yl)acetic acid was also uncovered.

Acetates↗
PubMed1993

Two-dimensional polyacrylamide gel electrophoresis of proteins labeled with the fluorophore monobromobimane prior to first-dimensional isoelectric focusing: imaging of the fluorescent protein spot patterns using a cooled charge-coupled device.

A new method for visualizing 2D protein spot patterns is described whereby proteins containing sulfhydryl groups are labeled with the fluorophore monobromobimane prior to the isoelectric focusing step of 2D polyacrylamide gel electrophoresis. The method requires the addition of a single reagent and a delay of only 15 min during sample preparation. High resolution spot patterns were obtained without the need for any post-electrophoretic gel handling. The gel patterns were imaged digitally immediately post-electrophoresis while the gels were still within their glass electrophoresis cassettes. The imaging system was based on a cooled charge-coupled device. The fluorescent spot patterns of proteins from the lymphoid cell-line IM9 were similar but not identical to silver-stained gel spot patterns of the same but underivatized sample. There was an overall increase (approx. 10%) in the number of spots visible on the fluorescent gels compared to those visible on the silver-stained gels.

Bridged Bicyclo Compounds↗