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At least 1,279 records · Page 71Linked to original sources
PubMed2006

Silver(I) complexes of fixed, polytopic bis(pyrazolyl)methane ligands: influence of ligand geometry on the formation of discrete metallacycles and coordination polymers.

Reactions of the arene-linked bis(pyrazolyl)methane ligands m-bis[bis(1-pyrazolyl)methyl]benzene, (m-[CH(pz)2]2C6H4, Lm), p-bis[bis(1-pyrazolyl)methyl]benzene, (p-[CH(pz)2]2C6H4, Lp), and 1,3,5-tris[bis(1-pyrazolyl)methyl]benzene (1,3,5-[CH(pz)2]3C6H3, L3) with AgX salts (pz = 1-pyrazolyl; X = BF4- or PF6-) yield two types of molecular motifs depending on the arrangement of the ligating sites about the central arene ring. Reactions of the m-phenylene-linked Lm with AgBF4 and AgPF6 afford complexes consisting of discrete, metallacyclic dications: [Ag2(mu-Lm)2](BF4)2 (1) and [Ag2(mu-Lm)2](PF6)2 (2). When the p-phenylene-linked Lp is treated with AgBF4 and AgPF6, acyclic, cationic coordination polymers are obtained: {[Ag(mu-Lp)]BF4}infinity (3) and {[Ag(mu-Lp)]PF6}infinity (4). Reaction of the ligand L3, containing three bis(pyrazolyl)methane units in a meta arrangement, with an equimolar amount of AgBF4 again yields discrete metallacyclic dications in which one bis(pyrazolyl)methane unit on each ligand remains unbound: [Ag2(mu-L3)2](BF4)2 (5). Treatment of L3 with an excess of AgBF4 affords a polymer of metallacycles, {[Ag3(mu-L3)2](BF4)3}infinity (6), with one of the bis(pyrazolyl)methane units on each ligand bound to a silver cation bridging two metallacycles. The supramolecular structures of the silver(I) complexes 1-6 are organized by noncovalent interactions, including weak hydrogen bonding, pi-pi, and anion-pi interactions.

Crystallography, X-Ray↗
PubMed1978

Demonstration of phosphates in calcium deposits: a modification of von Kossa's reaction.

It has been suggested that in von Kóss'as technic silver cations replace calcium bound to phosphate or carbonate groups and are then reduced to black metallic silver during exposure to light. However, in test tube experiments silver phosphate retains its yellow color for days. These differences between reactions of pure calcium phosphates and calcium deposits in tissues were emphasized already by von Kóssa; he regarded only the initial yellow coloration of calcium diagnostic for calcium phosphates and deplored the subsequent blackening caused by organic compounds. Von Kóssa's experiments were easily reproducible. A review of the literature showed that reduction of silver nitrate by organic compounds was well known in the 19th century. For histochemical studies of phosphates it was deemed desirable to avoid the formation of black by-products. Sections of paraffin-embedded human tissues were exposed to solutions of silver nitrate in subdued light or darkness then treated with sodium thiosulfate. Silver phosphate was yellow to yellowish brown; other tissue structures remained colorless. No darkening was observed in sections stored for eight years. Other compounds which form yellow silver salts, e.g. iodides and periodates, are unlikely to occur in paraffin sections of human tissues.

Aorta↗
PubMed1995

Scanning ion microscopy mapping of basement membrane elements and arterioles in the kidney after selenium-silver interaction.

The effects of selenium and silver salts was studied by scanning ionic microscopy during experimental argyria mapping of the different basement membrane elements. The ionic microscope (IMS 4F) was equipped with a high resolution spectrometer giving high spatial resolution on the image obtained. After long-term treatment with silver salt alone, silver and sulphur deposits were observed in the membranes. After administration of selenium and silver salt, it was possible to map nitrogen, sulphur, selenium and silver to the glomerular basement membrane as well as to the wall of the kidney arterioles. In the latter, sulphur, selenium and silver were localized only in the elastic laminae of the walls. This process of precipitation of silver deposits in the membrane can be interpreted as process of selenium "detoxification" of the organism.

Animals↗
PubMed1982

Selenium and kidney deposits in experimental argyria. Electron microscopy and microanalysis.

The conjugate effects of selenium and silver salts were studied in experimental renal argyria. Microanalysis has led to the localization of products of chemical reactions to Se and Ag in tissue sections. After prolonged treatment with Ag salts alone, there was Ag and S deposits in basal membranes. When Se and Ag were used together, the formation of these deposits in glomerular basal membranes was accelerated spectacularly. Electron probe microanalysis has shown that Se replaces S in silver deposits. Compared to its effect on other metals, Se was shown to have a complex action, characterized primarily by its toxic effect, favoring the appearance of symptoms of argyria.

Animals↗
PubMed1970

Electron microscopy of the ammoniacal silver reaction for histones in the erythropoietic cells of the chick.

The product of the postformalin ammoniacal silver reaction, which has been claimed to distinguish lysine-rich from arginine-rich histones with the light microscope on the basis of a color difference, was examined in developing erythroid cells of chick bone marrow with the electron microscope. Stem cells and early erythroblasts exhibit no, or little, ammoniacal silver reaction product, while small basophilic erythroblasts, polychromatophilic erythrocytes, and reticulocytes exhibit an increasing amount of reaction product as maturation proceeds. The reaction product is in the form of discrete electron-opaque particles associated with heterochromatin. The ammoniacal silver reaction in the erythroid cell series is interpreted as reflecting either the accumulation of newly synthesized arginine-rich histones or changes in the availability of reactive sites in preformed histones.

Animals↗
PubMed2005

Novel potentiometric immunosensor for determination of diphtheria antigen based on compound nanoparticles and bilayer two-dimensional sol-gel as matrices.

A novel method for fabrication of a diphtheria potentiometric immunosensor has been developed by means of self-assembling compound nanoparticles to a thiol-containing sol-gel network. A cleaned gold electrode was first immersed in a 3-mercaptopropyltrimethoxysilane (MPS) sol-gel solution to assemble a silica sol-gel monolayer. The silane entities were then polymerized into a two-dimensional sol-gel network (2D network) by dipping into aqueous NaOH. The second silane layer was formed by re-immersion in the MPS sol-gel solution overnight. The compound nanoparticles (nanocompounds) containing gold nanoparticles and silver nanoparticles were then chemisorbed on to the thiol groups of the second silane layer. Finally, diphtheria antibody (anti-Diph) was adsorbed on to the surface of the compound nanoparticles. The modified process was characterized by cyclic voltammetry (CV). Detection is based on the change in the potentiometric response before and after the antigen-antibody reaction. A direct potentiometric response to diphtheria antigen (Diph) was obtained from the immobilized diphtheria antibody. The potentiometric response of the resulting immunosensor was rapid and the linear range was from 22 to 800 ng mL-1 with the linear regression equation DeltaE=-79.5+69.4 log [Diph] and a detection limit of 3.7 ng mL-1 (at 3delta). Up to 19 successive assay cycles with retention of sensitivity were achieved for probes regenerated with 0.2 mol L-1 glycine-hydrochloric acid (Gly-HCl) buffer solution. Moreover, analytical results from several serum samples obtained using the developed technique were in satisfactory agreement with those given by the ELISA method, implying a promising alternative approach for detecting diphtheria antigen in clinical diagnosis.

Antibodies, Bacterial↗
PubMed2002

Cyclitol-based metal-complexing agents. Effect of the relative orientation of oxygen atoms in the ionophoric ring on the cation-binding ability of myo-inositol-based crown ethers.

myo-Inositol-derived crown ethers having varying relative orientations (1,3-diaxial, 1,2-diequatorial, and 1,2-axial-equatorial) of the oxygen atoms in the ionophoric ring were synthesized and the extent of their binding with picrates of alkali metals, ammonia, and silver were estimated. These crown ethers bind very well with potassium and silver picrates and show good to moderate binding toward lithium, sodium, cesium, and ammonium picrates. These myo-inositol-derived crown ethers exhibit very strong binding for silver, even though they do not have sulfur or nitrogen coordinating sites in them, which are known to have high affinity for silver. The ratio of binding constants for silver to other ions tested varies from 10(2) to 10(5). The ion selectivity and the strength of binding are dependent on the relative orientation of the oxygen atoms in the ionophoric ring as well as on the size of the macrocyclic ring.

Ammonia↗
PubMed1985

The effects of dietary L-ascorbic acid on the absorption and utilization of Na75SeO3 of silver-treated rats.

Male hooded lister rats of the Rowett Institute strain, treated with silver in the drinking water, were used to study the effects of L-ascorbic acid on the utilization of Na75SeO3. Silver treatment dramatically decreased the absorption of 75Se from the rat GI tract. An attempt was made to utilize the reducing ability of L-ascorbic acid upon the absorption of 75Se from the rat GI tract. Increasing concentrations of L-ascorbic acid slightly increased the amount of 75Se absorbed from the rat gut.

Animals↗
PubMed2006

Feasibility of static secondary ion mass spectrometry to study physicochemical interactions between organic components and silver in thermographic systems.

Chemical engineering of high-technology products requires elucidation of intermolecular interactions in complex materials. As part of an extensive study on thermographic systems, static secondary ion mass spectrometry (S-SIMS) was used to probe the physicochemical behaviour of active compounds, such as different tone modifiers and stabilisers, on silver. In particular, the feasibility of detecting adsorption and/or binding of individual additives and mixtures to silver was examined. Substrates prepared by sputter coating silver on silicon wafers were exposed to solutions of the studied compounds in 2-butanone. The signal intensities measured with S-SIMS for the ad-layers showed reproducibility to within 10%. Radical ions containing silver such as [M-H+Ag]+ * were used as evidence for the formation of bonds in the solid. Also the [M-H+2Ag]+ ions could be assigned to chemisorbed species while [M+Ag]+ ions could be formed by adduct ionisation of molecules with co-ejected Ag+ ions. The signal intensities of [M-H+Ag]+ * and [M-H+2Ag]+ ions were used to monitor the adsorption quantitatively as a function of time.

Journal Article↗
PubMed1997

Effect of the thyrotropin releasing hormone analogue posatirelin (RGH 2202) on microanatomical changes induced by lesions of the nucleus basalis magnocellularis in the rat.

The effect of 4 and 8 weeks treatment with 10 mg/kg/day of the thyrotropin releasing hormone analogue posatirelin (L-6-ketopiperidine-2-carbonyl-L-leucyl-proline amide) on microanatomical changes induced by monolateral and bilateral lesions of the nucleus basalis magnocellularis (NBM) were investigated. The following parameters were assessed in the frontal cortex and hippocampus of NBM-lesioned and sham-operated rats: 1) number of nerve cell and glial fibrillary acidic protein (GFAP)-immunoreactive astrocyte profiles; 2) density of silver-gold impregnated fibres; 3) density of choline acetyltransferase (ChAT)-immunoreactive fibres; 4) intensity of acetylcholinesterase (AChE) staining. In NBM-lesioned untreated rats, no changes in the number of nerve cell or of astrocyte profiles were found either in the frontal cortex or in the hippocampus. The only exception was a decrease in the number of granule neuron profiles in the dentate gyrus at 8 weeks after lesioning. Silver-gold impregnated fibres, which express the width of interneuronal connections, were reduced in the hippocampus but not in the frontal cortex of NBM-lesioned rats. ChAT immunoreactivity and AChE reactivity, which were localised respectively in nerve fibre-like structures and in the neuropil, were decreased in the frontal cortex but not in the hippocampus from the fourth week after NBM lesioning. Lesions did not change the number of ChAT-immunoreactive nerve fibres or intensity of AChE staining in the hippocampus. Treatment with posatirelin was without effect on the number of nerve cell profiles or of GFAP-immunoreactive astrocytes both at 4 and 8 weeks after NBM lesioning. Treatment with the compound increased the number of silver-gold impregnated fibres in the hippocampus of NBM-lesioned rats and restored in part ChAT immunoreactivity and AChE reactivity in the frontal cortex. These effects were noticeable in NBM-lesioned rats after 8 weeks of treatment. The possible significance of the neuroprotective effect elicited by posatirelin treatment after lesions of the NBM is discussed.

Acetylcholinesterase↗
PubMed2005

Coordination chemistry of a terpyridine-tris(pyrazolyl) ditopic ligand.

A new ditopic ligand, 4'-(4-(2,2,2-tris(1H-pyrazol-1-ido)ethoxymethyl)phenyl)-2,2':6',2''-terpyridine (pzt), has been prepared and its coordination chemistry studied. Metal ions with a preference for octahedral geometry form ML(2) complexes that are readily isolated and characterised, with the metal ion being bound to the terpyridine sites of both ligands. Other metal ions bind to the terpyridine site of just one ligand. In the case of silver(i), a dinuclear M(2)L(2) complex has been isolated in which each silver ion is coordinated to the terpyridine site of one ligand and to a single pyrazolyl donor group from the second ligand. Evidence for binding of metal ions to the tris(pyrazolyl) binding site was obtained by electrospray mass spectrometry and NMR techniques. The free ligand and three metal complexes, including the disilver complex, have been characterised by X-ray crystallographic techniques.

Binding Sites↗
PubMed2006

Exo-coordination-based supramolecular silver(I) complexes of S2O macrocycles: effect of ligand isomerism on the structural diversity.

An isomeric series of S2O macrocycles incorporating a xylyl group at the ortho (L1), meta (L2), and para (L3) positions were employed to examine the influence of the ring rigidity on silver(I) coordination modes in resulting supramolecular complexes (1-3); L1 and L3 afforded sandwich (1; Ag:L1 = 1:2) and infinite 1-D (3) complexes, respectively; otherwise, L2 gave the 1-D polymer (2a), 2:3 club sandwich (2b), and unique 2:4 bridged dinuclear complex (2c) complexes, in which their topologies vary with the solvent used.

Ligands↗
PubMed1970

Bacteriolytic enzymes from Staphylococcus aureus. Properties of the endo-beta-N-acetylglucosaminidase.

An extracellular bacteriolytic endo-beta-N-acetylglucosaminidase has been purified and its specificity of action has been investigated (Wadström & Hisatsune, 1970a,b). Some enzymic properties, such as optimum pH for enzyme activity on whole cells and cell walls of Micrococcus lysodeikticus and Staphylococcus aureus and optimum pH for stability, have been studied. The activity was maximum in 0.05m-tris-hydrochloric acid buffer, pH7.0. A higher ionic strength inhibited cell-wall hydrolysis. Since the crude and purified enzymes were found to be unstable on storage, the stabilizing and inhibiting effects of several compounds were investigated. Several heavy metal ions inactivated the enzyme at very low concentrations. Thiol compounds stabilized and thiol-reacting compounds partly inhibited the activity. Crude and purified glucosaminidase was found to be heat-stable at acidic pH and unstable at alkaline pH as previously found for several lysozymes (endo-beta-N-acetylmuramidases). Other properties of the staphylococcal enzyme and hen's-egg-white lysozyme have been compared, since the modes of action of the two are quite similar (Wadström & Hisatsune, 1970b).

Bacteriolysis↗
PubMed1999

In vitro antimicrobial activity of a new antiseptic central venous catheter.

A central venous catheter coated with a new antiseptic combination, silver chloride (AgCl) and benzalkonium chloride (BKC) in a polymer matrix, was developed. The antimicrobial efficacy and the ability to prevent surface colonization, after elution in both serum and saline, were evaluated and compared to catheters coated with silver sulfadiazine/chlorhexidine. The results of in vitro assays demonstrated that the AgCl-BKC coated catheters had a broad spectrum of activity against bacteria and C. albicans and prolonged antimicrobial activity for extraction periods of up to 30 days. These data suggest that AgCl-BKC coated catheters may provide another solution for reduction of catheter-related infections.

Anti-Bacterial Agents↗
PubMed1983

5-p-benzoquinonyl-2'-deoxyuridine 5'-phosphate: a possible mechanism-based inhibitor of thymidylate synthetase.

The title compound (1), designed as a suicide inhibitor of thymidylate synthetase, can be prepared by silver(II) oxide oxidative demethylation of the corresponding dimethoxyphenyl derivative. Compound 1 shows time-dependent inactivation of thymidylate synthetase (methotrexate-resistant Lactobacillus casei) and saturation kinetics, and the inactivation is responsive to substrate protection. The inactivation is not reversible on prolonged dialysis in attempts to remove the inhibitor. The rate constant for inactivation is 0.065 s-1; the dissociation constant (Ki) was estimated to be 2 microM. The kinetics of this inactivation are compared to inactivation caused by model thiol reagents that do not have affinity for the active site of thymidylate synthetase.

Deoxyuracil Nucleotides↗
PubMed1980

Interactions of vitamin E and selenium with mercury and silver.

It is well established that the toxicity of silver and methylmercury is suppressed by the presence of low levels of vitamin E or selenium in the diet, but little is known of the mechanisms involved. Silver induces a conditioned deficiency of selenium in rats, as shown by its effects on tissue levels of selenium and glutathione peroxidase (a selenoprotein), but methylmercury does not. Supplements of selenium do not decrease mercury levels in tissues of animals given methylmercury, and animals given selenium plus methylmercury may accumulate high levels of mercury without signs of toxicity. Although an equimolar accumulation of selenium and mercury in tissues sometimes occurs and could lead to mutual detoxification, such a coaccumulation is not always linked to protection. The only known functions of vitamin E and selenium are related to the prevention of oxidative damage. It is possible that their protective effects against heavy metals may involve such functions, thus accounting for the protection afforded by low levels of the nutrients against high levels of the metal toxicants.

Animals↗
PubMed2003

Relationship between composite contraction stress and leakage in Class V cavities.

PURPOSE: The purpose of this study was to determine the relationship between polymerization contraction stress and leakage in Class V composites. METHODS: A microfill (Heliomolar) and two minifill hybrid composites (Herculite, Z100) were tested. Maximum contraction stress (n = 5) for the composites was evaluated in a MTS machine at a C-factor of 3 (ratio of bonded to non-bonded surface area). Composite was placed in the gap between the surfaces of glass stubs that had been air abraded, silane treated and coated with a layer of resin adhesive. Specimens were light-cured through the top glass stub for 60 seconds and maximum force was recorded during the first 10 minutes. Leakage (n = 10) was evaluated by cutting cylindrical cavity preparations with all enamel margins (C-factor = 3) in bovine incisors. The cavities were treated with two layers of Scotchbond MP adhesive. Composites were applied in one increment, light-cured at the same intensity used in the stress tests, and immediately finished on SiC paper. After 1 day in water, the restorations were placed in silver nitrate, developed and evaluated as a single cross-section (2-D) and multiple cross-sections (3-D) for leakage: 0 (none), 1 (minimal leakage), 2 (to the DEJ), 3 (to line angle), 4 (along the pulpal wall). RESULTS: The maximum stresses (MPa) recorded were lowest for Heliomolar (7.0 +/- 0.4), intermediate for Herculite (10.5 +/- 0.6) and greatest for Z100 (11.6 +/- 1.3). 3-D leakage was as follows: Heliomolar--two specimens scored 1, seven scored 2 and one scored 3; Herculite--six scored 2 and four scored 3; Z100--eight scored 3 and two scored 4. The Kruskal-Wallis test showed a significant difference in leakage for the three composites (P < 0.05), and leakage was greater when evaluated in 3-D. The leakage results correlated with the stress values, i.e. composites with higher contraction stress showed more extensive marginal leakage.

Acrylic Resins↗