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This communication describes studies in which an azo hetero-Diels-Alder adduct was furnished in high regio- and enantioselectivity using azopyridine as a reagent and silver as a catalyst. The obtained hetero-Diels-Alder adduct was easily converted to the corresponding chiral 1,4-diamino alcohol.
The chemopreventive effects of 2 flavonoids (diosmin and hesperidin) on N-butyl-N-(4-hydroxybutyl)nitrosamine (OH-BBN)-induced urinary-bladder carcinogenesis were examined in male ICR mice. Animals were divided into 11 groups, and groups 1 to 7 were given OH-BBN (500 ppm) in the drinking water for 6 weeks. Groups 2 to 4 were fed diets containing the test compounds (group 2, 1000 ppm diosmin; group 3, 1000 ppm hesperidin; group 4,900 ppm diosmin + 100 ppm hesperidin) for 8 weeks during the initiation phase, while groups 5 to 7 were fed these diets, respectively, for 24 weeks during the post-initiation phase. Groups 8 to 11 were controls, given only the test compounds or untreated basal diets throughout the experiment (weeks 1 to 32). The incidence of bladder lesions and cell-proliferation activity estimated by enumeration of silver-stained nucleolar-organizer-region-associated proteins (AgNORs) and by the 5-bromodeoxyuridine (BUdR)-labeling index was compared among the groups. Feeding of the test compounds, singly or in combination, during both phases caused a significant reduction in the frequency of bladder carcinoma and preneoplasia. Dietary administration of these compounds significantly decreased the AgNOR count and the BUdR-labeling index of various bladder lesions. These findings suggest that the flavonoids diosmin and hesperidin, individually and in combination, are effective in inhibiting chemical carcinogenesis of the bladder, and that such inhibition might be partly related to suppression of cell proliferation.
The three regioisomers of methyl alpha-L-arabinofuranobioside, namely methyl O-alpha-L-arabinofuranosyl-(1-->2)-alpha-L-arabinofuranoside, methyl O-alpha-L-arabinofuranosyl-(1-->3)-alpha-L-arabinofuranoside, and methyl O-alpha-L-arabinofuranosyl-(1-->5)-alpha-L-arabinofuranoside, were synthesized for use as substrates in studies of the specificity of alpha-L-arabinofuranosidase. The regiospecifically protected precursors, namely methyl 3,5-di-O-benzoyl-alpha-L-arabinofuranoside, methyl 2,5-di-O-benzyl-alpha-L-arabinofuranoside, and methyl 2,3-di-O-benzoyl-alpha-L-arabinofuranoside, were prepared from 2,3,5-tri-O-benzoyl-alpha-L-arabinofuranosyl chloride (4) and methyl 5-O-trityl-alpha-L-arabinofuranoside, respectively, and glycosylated with 4 in the presence of silver trifluoromethanesulfonate and s-collidine. 1H and 13C NMR data for all compounds are presented.
Methyl 2,4-di-O-benzoyl-alpha-L-rhamnopyranoside (1) furnished a crystalline 3-O-bromoacetyl derivative that was treated with the dichloromethyl methyl ether-ZnCl2 reagent to give 2,4-di-O-benzoyl-3-O-bromoacetyl-alpha-L-rhamnopyranosyl chloride (3). Compounds 1 and 3 were condensed under the conditions of base-deficient, silver trifluoromethanesulfonate-mediated glycosylation to give a fully protected rhamnobioside, which on O-debromoacetylation afforded the disaccharide nucleophile 10. Similar condensation of 3 with methyl 3-O-benzoyl-4,6-O-benzylidene-alpha-D-galactopyranoside, followed by O-debromoacetylation and condensation of the thus formed methyl O-(2,4-di-O-benzoyl-alpha-L-rhamnopyranosyl)-(1----2)-4,6-O-benzylidene- 3-O-benzoyl-alpha-D-galactopyranoside again with 3, gave the trisaccharide glycoside. Subsequent O-debromoacetylation gave 17, having only HO-3(3) unsubstituted. Silver perchlorate-mediated glycosylations of 1, 10, and 17 with 3,4,6-tri-O-acetyl-2-azido-2-deoxy-alpha-D-glucopyranosyl chloride afforded, with high alpha stereoselectivity, protected di-, tri-, and tetra-saccharide glycosides. Subsequent hydrogenation, followed by N-acetylation and O-deacylation, afforded three oligosaccharide glycosides having nonreducing terminal 2-acetamido-2-deoxy-alpha-D-glucopyranosyl residues and comprising successively larger portions of the repeating unit of Shigella dysenteriae type 1 O-antigen.
Efficient syntheses of three [13C]methyl 2-[15N]amino-2-deoxy-beta-D-glucopyranoside derivatives are described. Amination of the D-glucal with (saltmen)Mn(15N) proceeded with 11:1 stereoselectivity favoring the gluco configuration; subsequent methylation of the [15N]lactol using [13C]iodomethane and silver(I) oxide afforded the doubly labeled beta glucoside in high yield. This compound served as the common precursor for three [13C]methyl 2-[15N]aminoglucosides: (2-[15N]trifluoroacetyl-), (2-[15N]acetyl-), and (2-[15N]azido-). Selected heteronuclear coupling constants are reported.
The chemical synthesis of beta-D-GalpNAc-(1-->4)-beta-D-GlcpNAc- (1-->3)-alpha-D-Galp-(1-->O)-(CH2)5NH2 is described. This structure represents the nonfucosylated backbone trisaccharide of the glycocalyx glycan of the cercarial stage of the parasite Schistosoma mansoni. Synthesis of the trisaccharide was achieved via a stepwise coupling approach. 5-Azidopentyl 4-O-acetyl-2,6-di-O-benzyl-alpha-D-galactopyranoside was condensed with ethyl 6-O-benzyl-2-deoxy-3,4-di-O-dimethylisopropylsilyl- 2-phthalimido-1-thio-beta-D-glucopyranoside, using N-iodosuccinimide and silver trifluoromethanesulfonate as a catalyst system, followed by the removal of the silyl ether groups to afford a disaccharide acceptor. Coupling of ethyl 4,6-di-O-acetyl-3-O- allyloxycarbonyl-2-deoxy-2-phthalimido-1-thio-beta-D-galactopyrano side to the disaccharide acceptor, using methylsulfenyl bromide and silver trifluoromethanesulfonate as a catalyst system, gave a protected trisaccharide. Deprotection of this compound yielded the target structure.
Mepitel is a new grid like silicone coated nylon dressing containing no additional biological compounds. We describe a prospective randomized pilot study comparing Mepitel to the standard silver sulfadiazine cream (Flamazine) dressing for the topical treatment of paediatric burns. Seventy-six children presenting within 24 h of injury with a non previously treated burn were randomly assigned to Mepitel treatment (group M) or Flamazine treatment (group F). Age, sex, surface area of burn and causal agent were noted at admission. The depth of the burn, cumulative number of dressings, presence or absence of a complete epithelial cover, infection, bleeding and allergy were noted at each dressing change. There were 41 children in group M and 35 children in group F. Five children were subsequently withdrawn from each group because they required skin grafting. Analysis of the above mentioned criteria showed no statistical difference between the two groups except for the healing time (group M: 7.58+/-3.12, group F: 11.26+/-6.02, p < 0.01) and the number of dressings (group M: 3.64+/-1.5, group F: 5.13+/-2.9, p < 0.05). Mepitel has proved to be an easy-to-remove dressing, adhering only to intact skin. The faster healing time found in the Mepitel group may be related to a direct effect of silicone on epithelial growth or to a decrease in surface-cell damage compared to the silver sulfadiazine group. This attractive product will be further assessed on a larger scale trial to confirm our observations.
We have shown that a scanning transmission electron microscope with a high brightness field emission source is capable of obtaining better than 3 A resolution using 30 to 40 keV electrons. Elastic dark field images of single atoms of uranium and mercury are shown which demonstrate this fact as determined by a modified Rayleigh criterion. Point-to-point micrograph resolution between 2.5 and 3.0 A is found in dark field images of micro-crystallites of uranium and thorium compounds. Furthermore, adequate contrast is available to observe single atoms as light as silver.
Single crystals of the title compound have been grown by annealing microcrystalline zinc cyanamide at 843 K in silver crucibles. Zn(CN(2)) crystallizes as colourless prisms. The crystal structure is composed of corner-linked ZnN(4/2) tetrahedra. Carbon and nitrogen form (CN(2))(2-) dumb-bells with the C atom on a twofold axis. Nitrogen is approximately trigonally planar, coordinated by two Zn atoms and one C atom.
(1,4,7-Trithiacyclononane)silver trifluoromethanesulfonate crystallizes in a tetrameric form from nitromethane, to give the title compound, [Ag(4)(C(6)H(12)S(3))(4)](CF(3)SO(3))(4) x 2CH(3)NO(2). The complex cation consists of four [AgL]+ units (L is 1,4,7-trithiacyclononane), with four Ag-S-Ag bridges forming a cyclic tetramer. The almost planar Ag(4)S(4) ring takes an octagonal form.
In this work we study the feasibility of using silver halide sensitized gelatin based on PFG-01 (Slavich) emulsions to construct uniaxial compound lenses. This processing is able to introduce variations in the thickness and refractive index of the emulsion. We prove that these changes are not sufficient to provide the observed variations in Bragg conditions in the reconstruction and that a shear-type effect must exist to explain the performance of processed emulsions. We study the characteristics of a compound lens, obtaining acceptable image quality, good resolution, and the typical field limitation of volume holographic elements.
The synthesis of the title compound and 1D-(1,3,5/2,4)-4-acetamido-5-amino-3-O-(beta-D-glucopyranosyluronic acid)- 1,2,3-cyclohexanetriol [sequence: see text] is described. Starting from methyl 2-acetamido-2-deoxy-alpha-D-glucopyranoside 2L-(2,4,5/3)-4-acetamido-3-benzoyloxy-2-benzyloxy-5- hydroxycyclohexanone [sequence: see text] was prepared via a series of transformations including the regioselective ring opening of the benzylidene acetal and the mercury(II)-catalyzed carbocyclic ring closure reaction of 5-enopyranoside. Stereoselective reduction of ketone 11 with NaBH(OAc)3 gave 1D-(1,2,4/3,5)-2-acetamido-3-O-benzoyl-4-O-benzyl-1,3,4,5- cyclohexanetetrol [sequence: see text] (88%), which was then converted into 1D-(1,3,5/2,4)-4-acetamido-5-azido-3-O-benzoyl-2-O- benzyl-1-O-pivaloyl-1,2,3-cyclohexanetriol [sequence: see text] through selective 5-OH protection, 1-O-mesylation, and subsequent azide displacement. Saponification and hydrogenation of this gave the title compound. Selective O-debenzoylation with 1.1 equiv of K2CO3 in MeOH gave 1D-(1,3,5/2,4)-4-acetamido-5-azido-2-O-benzyl-1-O- pivaloyl-1,2,3-cyclohexanetriol [sequence: see text] (73%). Glycosylation of this compound with methyl (2,3,4-tri-O-acetyl-alpha-D-glucopyranosyl bromide) uronate in Ch2Cl2, using silver triflate as the promoter, afforded 1D-(1,3,5/2,4)-4-acetamido-5-azido-2-O-benzyl-3-O-(methyl 2,3,4-tri-O-acetyl-beta-D-glucopyranosyluronate)-1-O- pivaloyl-1,2,3-cyclohexanetriol [sequence: see text] and subsequent hydrogenation of this compound gave the basic pseudo-disaccharide.
A quick, sensitive, and MALDI-TOF MS compatible silver staining method, namely Eriochrome black T (EBT)-silver method, is described. The method can detect 0.05-0.2 ng protein within 60 min in SDS-PAGE gels. EBT dye was used as a silver ion sensitizer having reducing power for silver ions.
OBJECTIVES: This study used cyclic voltammetry to examine the effect of the composition of dental amalgams on their electrochemical behavior, including reactions occurring outside of oral conditions. METHODS: Amalgams (residual mercury 47.5%) were prepared using two low-copper (3 wt% Cu) powders and five high-copper powders (40-80 wt% Ag, 12-30 wt% Cu) with and without zinc (1.5 wt%). Cyclic voltammograms were obtained at 37 degrees C in 1.0% NaCl scanning at 2 mV/s in the potential range from -1.5 V to +0.8 V vs. Ag/AgCl. RESULTS: During the anodic scans, AgCl and Hg2Cl2 films were formed on all amalgams except the one with only 40 wt% Ag. In all high-copper amalgams, a prominent Cu (oxidation) peak was found at -0.1 V, indicating the release of copper during corrosion. Zinc affected the oxidation process for both low- and high-copper amalgams. When zinc was absent, a peak for Sn2+ oxidation appeared at -0.4 V. When zinc was present, a Sn4+ oxidation peak was revealed at -0.6 V. In some amalgams, there was evidence of the selective corrosion (pitting corrosion) of tin and copper. In the lowest silver-content amalgam, no protective films were formed, which is indicative of its poor corrosion resistance. As expected, in all the low-copper amalgams, an extreme increase in current density was recorded immediately at 0 V, due to the release of tin from gamma 2. SIGNIFICANCE: Cyclic voltammetry is useful for the rapid examination (less than an hour) of the electrochemical behavior of amalgams, specifically to obtain information on the formation of compounds and the sequences of electrochemical reactions.
Liquid chromatography-electrospray ionization mass spectrometry (LC-ESI-MS) using silver nitrate as a post-column reagent has been used for the determination of 10 polycyclic aromatic hydrocarbons (PAHs) in river water. In this method, after all the PAHs were separated by reversed-phase liquid chromatography, analytes formed complexes with silver cation by mixing with silver nitrate solution. The complexes then transfer the molecular ion, [M]+, of the PAHs by charge transfer using in source collision-induced dissociation. The positive ion ESI mass spectra of all PAHs tested in this study showed [M]+ as the base peak and abundant [M+Ag]+, [2M+Ag]- with very weak or no [2M+Ag]+. For the sample extraction, several solid-phase extraction parameters using the blue-chitin column were optimized. The limits of detection (S/N=3) of all PAHs for the spiked river water sample ranged from 0.001 to 0.03 ng/ml, and the detector responses were linear up to I ng/ml (correlation coefficients > or =0.0998). Repeatability and reproducibility were in the range from 4.3 to 6.8% and from 6.2 to 9.5%, respectively.
The coordination chemistry of the tetrakis(thiophosphinato)resorcinarene sulfur-donor ligands [(C6H2CH{CH2CH2Ph})4{OC(O)R}4{OP(=S)Ph2}4] (L), where R = OCH2Ph, 4-C6H4CH3, C6H11, C4H3S, or OCH2CCH, is reported. Both silver(I) and gold(I) form cationic complexes of the type [LM2]2+, in which the ligand acts as a bis(chelate) in forming complexes with linear S-M-S (M = Ag or Au) stereochemistry. Gold(I) also forms the unusual complex [L(AuCl)2][LAu2]2+, which forms a supramolecular polymer through intermolecular aurophilic attractions. Palladium(II) forms the complex [LPd2Cl2(mu-Cl)2], in which the dipalladium(II) unit extends the natural bowl structure of the resorcinarene. The solid-state and solution conformations of the complexes, as determined by X-ray structure determination and NMR spectroscopy, respectively, are similar, but several complexes were found to exhibit dynamic behavior in solution, involving either conformational mobility of the resorcinarene unit or intermolecular ligand exchange.
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Recent advances in gold technology have led to probes with improved properties and performance for cell biologists: higher labeling density, better sensitivity, and greater penetration into tissues. Gold clusters, such as the 1.4-nm Nanogold, are gold compounds that can be covalently linked to Fab' antibody fragments, making small and stable probes. Silver enhancement then makes these small gold particles easily visible by EM, LM, and directly by eye. Another advance is the combination of fluorescent and gold probes for correlative microscopy. Chemical crosslinking of gold particles to many biologically active molecules has made possible many novel probes, such as gold-lipids, gold-Ni-NTA, and gold-ATP.