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At least 127 records · Page 7Linked to original sources
PubMed2006

Synthesis and characterization of stable organosols of silver nanoparticles by electrochemical dissolution of silver in DMSO.

Stable organosols of silver nanoparticles (AgNPs) without any capping agents have been synthesized by an electrochemical dissolution of a sacrificing silver electrode in dimethyl sulfoxide (DMSO). The peak at 425 +/- 5 nm observed in the UV-vis spectra was attributed to the surface plasmon resonance for silver. The formation of nanoparticles of silver was confirmed by X-ray diffraction analysis (XRD). In TEM, three ranges of particle size were observed, namely, 3.75 +/- 0.8, 6.25 +/- 0.5, and 9.25 +/- 0.3 nm. The correlation among these sizes was explained by a new model based on a droplet coalition. Based on that, sizes correlation fits very well in the empirical formula 5d(1)(3)n' + (3 - n')d(2)(3) = d(3)(3) where d(1), d(2), and d(3) are three sizes of particles and n' is an integer having values 0, 1, 2, 3, .... The sols prepared in DMSO were stable against flocculation for months. An unusual solution stability without any capping agents was attributed to the formation of Ag(I)DMSO complex on particle surface, which was confirmed by FTIR, fluorescence spectroscopy, and thermal analysis.

Dimethyl Sulfoxide↗
PubMed2006

Study of the affinity of thermographic additives for silver by time-of-flight static secondary ion mass spectrometry and surface-enhanced Raman spectroscopy on silver nanoparticles.

Detection of the interactions between low molecular weight organic compounds and metals in the form of sols on a nanoscale is analytically challenging. This study aims to provide experimental evidence using a combination of UV-Vis absorption spectrometry, surface-enhanced Raman spectrometry (SERS), and static secondary ion mass spectrometry (S-SIMS). The field of application is thermography where silver images are formed via heat-catalyzed reactions. Several organic compounds called tone modifiers and stabilizers are used in thermographic materials for the optimization of the image quality. With exploitation of the strengths of each of the above-mentioned methods, an affinity ranking of several tone modifiers and a stabilizer was established on the basis of competitive adsorption experiments using different model systems. Specifically, silver sols, SERS probes, and sputter-coated silver substrates were exposed to systems with one or two additives. The UV-Vis results provided insight on the aggregation of silver nanoparticles in a hydrosol, which was necessary for the interpretation of the SERS data. Both SERS and S-SIMS measurements led to a similar ranking of the relative affinity of the additives in two components, which was largely consistent with empirical knowledge derived from macroscopic behavior.

Heterocyclic Compounds, 2-Ring↗
PubMedDate not supplied

Comparison of silver-coated dressing (Acticoat), chlorhexidine acetate 0.5% (Bactigrass), and silver sulfadiazine 1% (Silverdin) for topical antibacterial effect in Pseudomonas aeruginosa-contaminated, full-skin thickness burn wounds in rats.

Acticoat (Smith and Nephew, Istanbul, Turkey), chlorhexidine acetate 0.5%, and silver sulfadiazine 1% were compared to assess the antibacterial effect of their application on experimental burn wounds in contaminated with Pseudomonas aeruginosa in rats. All treatment modalities were effective against P. aeruginosa because there were significant differences between treatment groups and control groups. The mean eschar concentrations did not differ significantly between Acticoat and chlorhexidine acetate groups, but there were significant differences between the silver sulfadiazine group and the other treatment groups, indicating that silver sulfadiazine significantly eliminated P. aeruginosa more effectively in the tissues than did the other two agents. All treatment modalities were sufficient to prevent the P. aeruginosa from invading to the muscle and from causing systemic infection. In conclusion, silver sulfadiazine is the most effective agent in the treatment of the P. aeruginosa-contaminated burn wounds; Acticoat can be considered as a treatment choice because of its peculiar ability of limiting the frequency of replacing wound dressings.

Administration, Topical↗
PubMed2004

Topical treatment of partial thickness burns by silver sulfadiazine plus hyaluronic acid compared to silver sulfadiazine alone: a double-blind, clinical study.

Since its introduction into clinical practice in 1967 by Charles Fox Jr., silver sulfadiazine has been the gold standard for topical burn therapy. The addition to it of hyaluronic acid, which forms a substantial part of the human tissue intercellular matrix, is aimed at overcoming one of its very few disadvantages, i.e. prolongation of the wound re-epithelialization process. Since both hyaluronic acid and silver sulfadiazine have been used in therapy for decades and their efficacy is well documented, a topical treatment combining these two agents was formulated. The aim of the study was to investigate the efficacy and tolerability of a cream containing a hyaluronic acid/silver sulfadiazine fixed combination, compared with silver sulfadiazine cream alone, for the treatment of superficial and deep second-degree burns in a prospective, double-blind, controlled clinical study. The findings of the study confirmed that the association of the two compounds in a new topical treatment significantly reduced the healing time and significantly accelerated the reduction of local edema occurring shortly after injury. Furthermore, this new hyaluronic acid and silver sulfadiazine formulation has proven to have favorable antibacterial, anti-edematous and local analgesic effects, together with a clear stimulatory activity on the re-epithelialization process. This product may, therefore, significantly enrich the assortment of topical medications available for the treatment of burns and skin defects of other origin.

Administration, Topical↗
PubMedDate not supplied

[Surface-enhanced Raman spectroscopy of biopolymers: membrane proteins, bacteriorhodopsin and rhodopsin adsorbed on silver electrodes and silver hydrosols].

Surface-enhanced Raman (SER) spectra of purple membranes of Halobacterium halobium and photoreceptor disks of the rod outer segments adsorbed on silver hydrosols were analysed. It has been shown that the intensity of SER spectra of bacterial and visual rhodopsins increases 5 X 10(4) times at adsorption. Concentration relationship of the signal intensity of SER spectra has the maximum at bacteriorhodopsin concentration about 2 X 10(-7) M. It has been shown that adsorption on silver hydrosol leads to fixation of light-induced photochemical transformations in bacterial and visual rhodopsins. Adsorption on the "smooth" electrodes at the potential of the zero charge of silver does not affect the photocycle of bacteriorhodopsin. An increase or decrease of the electrode potential relative to the zero charge point of silver leads to the accumulation of kinetic intermediate K610 and a decrease of the concentration of the form BRh570. It has been shown that on the "smooth" electrode primarily the long-range component of the SER mechanism is realized. Bands corresponding to the vibrations of the atom groups directly contacting with the metal are mainly intensified after redox cycle which increases the concentration of chemosorption centres. A conclusion is drawn that the method of SER spectroscopy of biomolecules adsorbed on "smooth" electrodes, permits obtaining information similar to that obtained from the analysis of Raman spectra of unadsorbed molecules, but at concentrations by two orders less. Adsorption on the electrodes treated with the help of redox cycle permits to obtain highly oriented preparations and to study topography of biopolymers in water solutions and suspensions.

Bacteriorhodopsins↗
PubMed1993

Application of silver acetate autometallography and gold-silver staining methods for in situ DNA hybridization.

In situ hybridization using biotinylated DNA probes has become an important tool in histopathology. It is well known that the sensitivity of the methods used to demonstrate viral DNA in formalin-fixed and paraffin-embedded specimen depends strongly on the detection system used. In the present study, an optimized in situ DNA hybridization protocol was combined with four different approaches of gold-silver staining methods. For silver enhancement, the recently described method of silver acetate autometallography, a technique allowing highly efficient development without the necessity of dark room illumination has been used. The most efficient detection method found in our experiments was the use of gold-adsorbed anti-biotin antibodies with subsequent silver enhancement. This staining procedure can be completed in 5 hours including hybridization and is a highly sensitive alternative to peroxidase and alkaline phosphatase detection systems.

Cytomegalovirus↗
PubMed2001

Surface-Enhanced Raman Scattering of Rhodamine 123 in Silver Hydrosols and in Langmuir-Blodgett Films on Silver Islands.

Surface-enhanced Raman scattering(SERS) of the Rhodamine 123 (Rh 123) molecule on ion-induced silver colloids has been studied. A time-dependent study of the SER spectra at a particular pH confirms charge transfer interaction between the probe molecule and the metal. The SER spectra of Rh 123 in Ag sol is compared with that of the molecules organized in a monolayer on silver island films by the Langmuir-Blodgett (LB) technique. The origin of high SERS activity of Rh 123 molecules in a monolayer on a silver island film is shown to be due to physisorption whereas in the ion-induced colloidal SERS both physisorption and chemisorption machanisms are involved. From these results, the contribution of charge transfer interaction to SERS in Ag sol has been estimated. In monolayer SERS, all the in-plane and out-of-plane (of xanthene ring) modes are more or less equally enhanced. This indicates that the xanthene plane of Rh 123 molecule organized in a LB film is oriented neither flat nor perpendicular to the silver island surface but is tilted. Copyright 2001 Academic Press.

Journal Article↗
PubMed2006

Templated synthesis of silver nanowires based on the layer-by-layer assembly of silver with dithiodipropionic acid molecules as spacers.

The layer-by-layer assembly of silver nanoclusters with 3,3'-dithiodipropionic acid (DTDPA) as spacers was prepared through self-assembly on a gold foil and has been characterized by cyclic voltammetric and AFM techniques. The DTDPA molecules acting as spacers between the layers of silver serve as molecular interconnects for the four layers prepared in this work. The organization of layers was found to decrease with an increase in the number of layers. The layer-by-layer assembly of silver clusters motivated us to prepare silver nanowires stabilized by the bifunctional molecules DTDPA through template synthesis using cellulose nitrate membranes. The nanostructures formed by this method were characterized by SEM, TEM, AFM, FTIR, CV, and photoluminescence studies. It is observed that the DTDPA molecules, instead of forming molecular interconnects, protect the structures by self-assembling themselves along the edges of the nanostructures. The concept of self-assembly protecting the nanostructures is demonstrated in this work.

Journal Article↗
PubMed2006

Anion- and solvent-directed assembly in silver bis(thioimidazolyl)methane chemistry and the silver-sulfur interaction.

The effect of metal complexation on the structure and properties of the electroactive bis(1-methylthioimidazolyl)methane linkage isomers CH2(N-tim)2 (L1) and CH2(S-tim)2 (L2) has been explored. Coordination polymers {[Ag(L1)2]X}n (X = BF4, PF6) are formed by bridging L1 between tetrahedral silver centers giving two-dimensional cationic sheets composed of AgS(4) linkages; the anions are sandwiched between sheets. Cyclic dimers {[Ag2(L2)2]X2} (X = BF4, PF6, OSO2CF3) are formed when L2:AgX ratios are lower than 1.5. When L2:AgPF6 was 1.5 or higher, the complex [Ag4(L2)5](PF5)4 could be isolated as a solvate. The NMR, IR, electrochemical, and ESI+ mass spectral data of this latter compound indicate that extensive dissociation to the cyclic dimer and free ligand occurs in solution. Finally, a Cambridge Structural Database search was performed to provide insight into reasonable silver-sulfur bond distances, since literature values appeared to vary widely between 2.3 and 3.2 A. It was found that these distances increase with increasing coordination number of silver. The average distances for 2-, 3-, 4-, 5-, and 6-coordinate silver were found to be 2.40, 2.52, 2.62, 2.70, and 2.75 A, respectively.

Journal Article↗
PubMed2002

Reversible conversion of nanoparticles of metallic silver and silver oxide in ultrathin TiO2 films: a chemical transformation in nano-space.

The in-situ interconversion of silver and silver oxide nanoparticles was achieved in ultrathin TiO2 films using hydrogen and oxygen plasmas as dry redox reagents. Absorption spectroscopy and transmission electron microscopy showed that the chemical transformation gave rise to narrowing of size distributions of both silver and silver oxide nanoparticles upon repeated interconversion.

Journal Article↗
PubMed2000

New insights on the structure of the mouse silver locus and on the function of the silver protein.

The melanosomal proteins encoded by the silver locus play important roles in melanogenesis. The human locus yields two proteins, PMEL17 and GP100, by alternative mRNA splicing. The mouse si locus was reported to encode a Pmel17 protein, and later gp87, a GP100 homologue. When we re-examined the products of wild-type and silver-mutant mouse si loci, RT-PCR of wild-type RNA and genomic DNA sequence accounted for gp87 but excluded the occurrence of Pmel17. Analysis of cDNA from the silver (si/si) melanocyte line, melan-si, showed that the pathogenic mutation is a G to A substitution at nt 1808, which yields a premature stop codon and a predicted protein truncated in the C-terminus. This was confirmed by reaction of a specific anti-gp87 antiserum with si/si melanocyte extracts. To further explore gp87 function, we compared the DHICA oxidase activity of extracts from B16, melan-si (heterozygous for the brown mutation and homozygous for the silver mutation) and Cloudman S91 cells (homozygous for the brown mutation), since both TRP1 and gp87 are thought to be involved in DHICA oxidation/polymerization. Cloudman extracts do not oxidize significantly DHICA and its methyl ester, supporting the involvement of native mouse TRP1 in DHICA oxidation. Extracts from B16 and melan-si do not show significant differences for the oxidation of free acid and methylated dihydroxyindoles, indicating that the mechanism is not decarboxylative. Melan-si extracts are very efficient in catalyzing dihydroxyindole oxidation, in spite of being heterozygous for the TRP1 mutation, consistent with a stablin effect for the wild-type gp87 protein. On the other hand, aggregated and degraded forms of that mutant gp87 protein are found in the cytosolic fraction of melan-si, suggesting that misrouting and aberrant processing of the gp87 and tyrosinase may also be related to the high DHICA oxidase activity of these melanocytes.

Alternative Splicing↗
PubMed1996

Formation of Atomically Flat Silver Films on GaAs with a "Silver Mean" Quasi Periodicity

A flat epitaxial silver film on a gallium arsenide [GaAs(110)] surface was synthesized in a two-step process. Deposition of a critical thickness of silver at low temperature led to the formation of a dense nanocluster film. Upon annealing, all atoms rearranged themselves into an atomically flat film. This silver film has a close-packed (111) structure modulated by a "silver mean" quasi-periodic sequence. The ability to grow such epitaxial overlayers of metals on semiconductors enables the testing of theoretical models and provides a connection between metal and semiconductor technologies.

Journal Article↗
PubMed2002

Silver-enhanced reduction of 2,3,5-triphenyl-2H-tetrazolium by semicarbazide for the spectrophotometric determination of traces of silver(I).

A sensitive spectrophotometric method for the determination of silver is described. The reaction involves a silver-enhanced reduction of 2,3,5-triphenyl-2H-tetrazolium chloride by semicarbazide hydrochloride to yield a pink-colored product with maximum absorption at 510 nm. Beer's law is obeyed in the concentration range of 0.02-0.34 microg cm(-3) of silver, and the molar absorptivity is 4.51 x 10(5) l mol(-1) cm(-1). The optical parameters, optimum reaction conditions and interference studies have been described. The method has been applied to the determination of silver in photographic film waste water and in synthetic samples.

Journal Article↗
PubMed1987

Localization of silver deposits on Pneumocystis carinii treated with Gomori's methenamine silver nitrate stain.

The question which portion of the pellicle of Pneumocystis carinii is actually stained by the Gomori's methenamine silver nitrate (GMS) method was solved with the aid of electron microscopy. Silver particles were specifically deposited on the electron-lucent middle layer of the precyst, cyst and ruptured cyst, whereas such deposition was not found on the pellicle of the trophozoite, probably due to the absence of the electron-lucent middle layer in the trophozoite. These deposits increased in proportion to the duration of staining and to the thickness of the lucent middle layer. Therefore, the lighter colored organisms as observed under the light microscope are considered to be the precysts because they have thinner GMS-positive middle layers than those of cysts. So-called parentheses-like structures or rings are one of the most characteristic light microscopic features of P. carinii cysts when stained with GMS. The present study indicates that these structures must be of cyst wall origin rather than of cytoplasm origin, because the thickened part of the cyst wall showed a dense deposition of silver particles, probably corresponding to the parentheses-like structure. On the other hand we also observed, in the endogeny form of trophozoite, a thin GMS-positive layer in the parent pellicle though this pellicle showed no differences from those of daughter and common trophozoites when observed by means of ultrathin section microscopy.

Animals↗
PubMed1984

Inhibition of adenosine triphosphatase in vitro by silver nitrate and silver sulfadiazine.

Inhibition of adenosine triphosphatase (ATPase) by silver nitrate (AgNO3) in vitro was studied in microsomal fractions or tissue homogenates of canine brain and kidney, and human kidney. In microsomal fractions, AgNO3 was an indiscriminate inhibitor of ouabain-sensitive (Na+ + K+ ATPase) and ouabain-insensitive (Mg2+ ATPase) activities with 50% inhibition obtaining at concentrations on the order of 10(-7) to 10(-6)M. The enzyme was protected by cysteine. Changing the concentrations of Na+, K+, H+, Mg2+ and ATP did not alter the fractional inhibition of Na+ + K+ ATPase by a constant concentration of AgNO3. An aqueous suspension of silver sulfadiazine had an inhibitory potency similar to AgNO3. It was concluded that silver gives a different pattern of Na+ + K+ ATPase inhibition than other metallic inhibitors of the enzyme so far examined.

Adenosine Triphosphatases↗
PubMed1991

Amplification of the in situ hybridization signal by silver postintensification: the biotin-dUTP-streptavidin-peroxidase diaminobenzidine-silver-gold detection system.

Frozen and vibratome sections from the adrenal gland of the rat were hybridized in situ using a biotinylated oligonucleotide probe specific for tyrosine hydroxylase (TH) messenger ribonucleic acid (mRNA). Hybridization was detected using the streptavidin-peroxidase-diaminobenzidine (DAB) system in combination with silver-gold postintensification. The signal appeared as a black coloration and was localized to the cytoplasm of catecholamine-synthesizing chromaffin cells in the adrenal medulla. This coloration was due to the deposition of the silver-gold intensified DAB chromogen onto the probe hybridized to mRNA in carrier organelles. Compared with the conventional peroxidase-DAB labelling, the silver-gold amplified version was more sensitive in detecting TH mRNA. Using this modification, we were able to adapt the procedure to electron microscopy, thereby further localizing the hybridized signal to ribosomes. Because this hybridization detection system produces grains, not just color, this method has the potential for measurement of changes in mRNA levels at the ultrastructural level.

3,3'-Diaminobenzidine↗
PubMed1994

Biocompatibility of silver-coated polyurethane catheters and silver-coated Dacron material.

The local effects of silver-coated polyurethane catheters and Dacron material were compared to uncoated polyurethane catheters and Dacron material in a long-term implantation test using rabbits. The tissue-implant interaction was analysed by investigating the type and number of inflammatory cells, capillaries, fat tissue, the extent of fibrosis, thickness of the fibrous capsule, number and distribution of silver particles, and the size of giant cells. Silver-coated and uncoated materials displayed comparable signs of inflammation and tissue reaction.

Animals↗
PubMed2003

Measurement of cytoplasmic copper, silver, and gold with a lux biosensor shows copper and silver, but not gold, efflux by the CopA ATPase of Escherichia coli.

Copper, silver, gold and other heavy metals are potentially toxic to cells. Copper is also essential and cellular levels must be carefully controlled. In contrast, there is no known biological role for silver or gold and they have not been recognized as metals that are under homeostatic control. Using a luminescent biosensor based of the Vibrio fischeri lux gene cluster under the control of the Escherichia coli copA promoter/CueR metal-responsive regulator, we could show that in E. coli, cytoplasmic copper and silver, but not gold, are regulated by the CopA ATPase, the major copper efflux pump.

Adenosine Triphosphatases↗