Molar Ratio Of Ag Research Articles

Bimetallic colloids of silver and copper in thin films: sol–gel synthesis and characterization

A sol–gel route to synthesize thin films containing alloy- and phase separated mixed-colloids of silver (Ag) and copper (Cu) has been developed. Ag–Cu alloy colloids with Ag:Cu molar ratios of 4:1–1:2 in the coatings were obtained by the addition of copper ions stabilized in a pre-hydrolyzed SiO 2-sol in the presence of hydroxylamine hydrochloride, to a colloidal silver sol stabilized by a polymer, followed by the reduction of Cu + ions under reducing atmosphere. After a thermal treatment at temperatures ranging from 150 to 550 °C, the coatings were characterized by ultraviolet–visible spectroscopy, X-ray diffraction and high-resolution transmission electron microscopy. Mixing of silver and copper as ions always led to the formation of Ag–Cu phase separated mixed colloids. For Ag–Cu alloy colloids absorption peak remains as a single peak as long as the molar ratio of Ag and Cu is less than 4:1, whereas two absorption peaks were obtained on increasing the copper concentration. This behavior was attributed to the limited miscibility of Ag and Cu. On the other hand, for Ag–Cu mixed colloids two plasmon peaks were obtained irrespective to their molar ratios.

Formation and characterization of Au–Ag bimetallic nanoparticles in water-in-oil microemulsions

Gold–silver bimetallic nanoparticles with varying mole fractions were synthesized in water-in-oil microemulsions of water/Aerosol OT/isooctane by the co-reduction of HAuCl4 and AgNO3 with hydrazine at 25 °C. TEM analysis revealed that the bimetallic nanoparticles were essentially monodisperse and had a mean diameter of 4–22 nm, increasing with an increase in the molar ratio of water to Aerosol OT (ω0) and Ag content. The UV/VIS absorption spectra of their solutions exhibited only one plasmon absorption and the absorption maximum of the plasmon band red-shifted almost linearly from 400 to 520 nm with increasing Au ∶ Ag molar ratio, revealing the formation of an alloy. Although the characteristic peaks for Au and Ag were too close to distinguish, the XRD analysis showed that the characteristic peaks for a Au–Ag bimetallic systems became broader and accordingly suggested the formation of bimetallic nanoparticles. The EDX analysis confirmed directly the formation of Au–Ag bimetallic nanoparticles. It showed that the composition of Au–Ag bimetallic nanoparticles was in good agreement with that of the feed solution but the outer layer of the particles was enriched in Ag. The HRTEM study indicated the resultant Au–Ag bimetallic nanoparticles contained single and multiple twins as well as stacking faults, and no mismatch was present. In addition, it was found that the formation rate of Au nanoparticles was much faster than that of Ag nanoparticles. This satisfactorily accounted for the composition distribution within a Au–Ag bimetallic nanoparticle.

Clinical evaluation (phase I) of a combination of two human monoclonal antibodies to HBV: Safety and antiviral properties

Treatment of chronic hepatitis B virus (HBV) infection with interferon alfa and lamivudine is characterized by lack of viral clearance, loss of response, or emergence of drug-resistant mutants. Thus, new and multiple drug approaches are needed. We have developed two fully human monoclonal antibodies, directed against different epitopes of hepatitis B surface antigen (HBsAg) that bind to all major HBV subtypes. A phase I clinical study was conducted to evaluate the safety, tolerability, and efficacy of a mixture of these two monoclonal antibodies, HBV-ABXTL. A total of 27 chronic HBV patients were enrolled. In part A of the study 15 patients in 5 cohorts received a single intravenous infusion of antibodies with doses ranging from 0.26 mg (260 IU) to 40 mg (40,000 IU). All patients completed 16 weeks of follow-up. In the second part of the study (part B), 12 patients in 4 cohorts received 4 weekly infusions of 10, 20, 40, or 80 mg each of HBV-ABXTL and were followed for 4 additional weeks. Administration of antibodies was well tolerated. Patients administered doses at an Ab:Ag molar ratio of 1:2 to 1:20 showed a rapid and significant decrease in HBsAg to undetectable levels, with a corresponding reduction of HBV-DNA levels. In part B, HBV-ABXTL induced a significant reduction in both HBsAg and HBV-DNA levels repeatedly after administration. In conclusion, these data suggest that HBV-ABXTL binds HBV particles and reduces serum viral titers and HBsAg levels. HBV-ABXTL could be combined with other monotherapies that are currently used to treat HBV carriers. (HEPATOLOGY 2002;35:673-679.)

Silica‐supported silver nano‐particles for surface‐enhanced Raman spectroscopy

AbstractWe have developed and prepared a new type of substrate by impregnating silica with silver for surface‐enhanced Raman scattering (SERS). The effects of several experimental conditions of preparation, including the drying temperature, the molar ratio of Ag to Si, the calcination time and the calcination temperature, were investigated and varied to give a better surface enhancement efficiency of the substrate. X‐ray diffraction and transmission electron microscopy were used to measure the relative abundance of silver metal and the size of silver particles in the substrates. The results provided useful information that would be helpful in explaining the surface‐enhanced performance of silica‐supported silver substrates prepared under different conditions. The SERS spectra of several organic dyes were used to demonstrate the performance of the silver–silica substrate. Copyright © 2001 John Wiley & Sons, Ltd.

Magnetoresistance of a (γ-Fe2O3)80Ag20 nanocomposite prepared in reverse micelles

The magnetic and transport properties of a (γ-Fe2O3)80Ag20 nanocomposite, prepared by a reverse micelle technique, have been studied. γ-Fe2O3 nanoparticles and Ag particles were individually synthesized in reverse micelles. The nanocomposite material was then prepared by mixing the two different particles in a γ-Fe2O3/Ag molar ratio 80/20. The morphology of the nanoparticles was examined with transmission electron microscopy. Mössbauer spectra revealed no obvious presence of any divalent iron. Zero field cooled and field cooled magnetic susceptibilities indicated a blocking temperature of about 40 K. Negative magnetoresistance was observed resembling that in ball milled γ-Fe2O3/Ag nanocomposites. However, the magnitude of the negative magnetoresistance is smaller and is ∼2.2% at 220 K and 9 T. Two possible mechanisms, spin-dependent hopping and tunneling across magnetic barriers, are discussed.

Abnormality detection method, abnormality detection apparatus, and solar cell power generating system using the same

Centimeter level AgCuAu composite nanowires were prepared by a solid-state ionics method under a direct current electric field (DCEF) using fast ionic conductor RbAg4I5 films and vacuum thermal evaporation method. The surface morphology and chemical composition of the AuAgCu composite nanowires were characterized by scanning electron microscopy (SEM) and energy dispersive spectrometer (EDS), respectively. Raman enhancement performance of the AgCuAu composite nanowires substrates was detected by Rhodamine 6G (R6G) aqueous solutions as probe molecules. Long-range order and short-range order AgCuAu composite nanowires with the length of 1 cm were prepared. The nanowires were bamboo-shaped with high surface roughness and the diameters of nanowires ranged from 60 to 100 nm. The molar ratio of Ag:Cu:Au in composite nanowires is 15:2:1. The intrinsic Raman peaks of 10−16 mol/L R6G at 612, 773, 1125, 1182, 1307, 1361, 1418, 1506, 1545, 1575, 1597, 1650 cm−1 are all present when AgCuAu composite nanowires were used as the SERS substrates.

Binding of model soluble immune complexes to modified C-reactive protein.

Abstract We have identified a binding interaction between a modified form of C-reactive protein (mCRP) and model immune complexes. We have characterized these interactions in terms of their relative affinity, specificity, pH dependence, and recognition site on mCRP. First, binding isotherms were generated for the reaction of immobilized mCRP with heat-aggregated IgG (HAG) which gave an estimate for the value of the dissociation constant, Kd, of 1.6 nM. Second, competitive binding assays were performed using immobilized HAG to determine the relative affinity (IC50) for the interaction between HAG or monomeric IgG and mCRP in the fluid phase. While the binding of HAG to mCRP occurred with high affinity (IC50=0.72 nM), the binding of monomeric IgG to mCRP occurred with >2000-fold lower affinity (IC50>1.66 muM). Third, immune complex binding to immobilized mCRP was studied using defined ratios of horseradish peroxidase and rabbit anti-peroxidase Ab. The binding of these complexes to mCRP was strongly pH dependent, with a maximum at pH 5.5. At this optimal pH, preformed peroxidase-antiperoxidase immune complexes (approximately 2:3 Ab:Ag molar ratio) were shown to bind immobilized mCRP with a Kd of 111 nM. Fourth, using mCRP-specific mAbs, HAG and peroxidase- antiperoxidase binding sites were localized to CRP sequences to 130 to 138 and 200 to 206. Since inflammatory processes often cause microenvironments to become acidic, and since mCRP selectively binds immune complexes at acidic pH, we propose that mCRP mediates the specific binding of immune complexes in vivo and potentiates effector reactions for immune complex removal.

Trace Metal Concentrations in the Surf Zone and in Coastal Waters off Baja California, Mexico

Pronounced spatial gradients were observed in trace element concentrations (Cd, Co, Cu, and Ni) in nearshore surf zone (<100 m offshore) and coastal (5−45 km offshore) waters off Baja California, Mexico. The ranges of metal concentrations in those waters were 0.034−0.26 nM for Cd, 0.022−0.59 nM for Co, 0.93−3.6 nM for Cu, and 3.6−6.4 nM for Ni. Metal concentrations exhibited offshore gradients, with the highest levels nearshore. Metal:salinity, metal:nutrient, and metal:metal relationships indicated that the relatively high nearshore concentrations were caused by upwelling (Cd and Ni) and by benthic particle resuspension and diagenetic remobilization (Co and Cu). The relatively low offshore concentration levels appeared to be caused, in part, by the intrusion of oceanic waters from the North Pacific Central Gyre, as evidenced by similarities in the molar ratios of Ag:Cu in coastal waters off Baja California (9.0 × 10-3) and in subtropical oceanic waters off central Mexico (9.6 × 10-3). This was also consi...

Effect of Dietary Cadmium on Growth, Survival, and Tissue Concentrations of Cadmium, Zinc, Copper, and Silver in Juvenile American Lobster (Homarus americanus)

The addition of as much as 45 mg Cd/kg to a crab-based diet did not significantly affect growth or survival of juvenile American lobster (Homarus americanus) fed for 17 wk. The addition of Cd to the crab-based diet destroyed the highly significant relationship observed in nature between Cu and Ag concentrations in the digestive gland. Cd, Zn, and Cu in the crab-based diet were taken up by the digestive gland more efficiently than these metals added to the casein-based diet. Cu, Zn, and Ag concentrations in tail muscle were not affected by dietary Cd. Tissue mean molar ratios of metals (normalized to Cu and Ag) and dietary Cd ic crab-based diets showed a significant (p &lt; 0.05) logarithmic relationship between dietary Cd levels and Cu/Ag (or Ag/Cu) ratios in both the tail muscle and digestive gland and Cd/Cu and Cd/Ag ratios in the digestive gland. A linear relationship was observed between Cd levels in crab-based diets and Cd/Cu, Cd/Ag, and Zn/Ag ratios in tail muscle. The absence of ascorbic acid (vitamin C) in the diet increased the uptake of Cd by the digestive gland and had an interactive effect on mean molar ratios of Cd, Cu, and Ag in the digestive gland.

Potentiometric study of the solid state ion-exchange reaction between α-AgI and β″-alumina

The ion-exchange reaction between β″-alumina and solid α-AgI was investigated by measuring the EMF of a galvanic cell with a β″-alumina solid electrolyte. The following cell was assembled and EMF measurements were taken in a temperature range between 342 to 816 K: Mo, Na(s, 1)| β″-alumina|Ag+AgI+ β″-alumina, Mo (I). Ag, AgI and β″- alumina powders were mixed in a molar ratio of Ag : AgI : Na (in β″-alumina powder) of 1.00 : 1.00 : 1.00. The cell was heated and maintained at 630 K for 30 d. The ion-exchange between Ag + ion in α-AgI and Na + ion in β″-alumina powder gradually proceeded and formed two solid solutions of (Ag + −Na + )I − and (Na + −Ag + )-β″-alumina. The resulting EMF was higher than that of cell ( II) : Mo, Na(s, 1)| β″-alumina|NaI+Ag+AgI, Mo(II). The 30 days retention at 630 K gave a cell EMF of 2.1370 V which was higher than the EMF of cell (II) by 9.6 mV. When the cell temperature was decreased below 600 K, a NaI saturated with AgI, (Na + −Ag + )I − sat. phase appeared and the EMFs of cell (I) agreed with the EMFs of cell (II). By heating the cell to a particular temperature on the liquidus line on the AgI side of the AgINaI system, a liquid phase appeared and the ion-exchange between α-AgI and β″-alumina smoothly proceeded via the liquid. After that, two kinds of three-phase-equilibria of (Ag −Na−I) sat.+(Ag + −Na + )I − sat.+(Na + −Ag + )I − sat. and (Ag −Na−I) sat.+ (Ag + −Na + )I − sat.+liquid (Ag + −Na + )I − were attained below and above 657 K, respectively. Then, the EMFs of cell (I) agreed with the value of cell (II) below 657 K.

Flotation and spectrophotometric determination of silver with 4-(p-nitrophenylazo)-2-amino-3-pyridinol

A sensitive flotation-spectrophotometric method, based on the complex formed between Ag(I) and 4-(p-nitrophenylazo)-2-amino-3-pyridinol is described. The complex precipitates when the aqueous solution is shaken with benzene, and the solid formed is then dissolved in dimethylformamide. The molar absorptivity of the resulting solution is 10.7×104l·mole−1·cm−1 at 605 nm. Beer's law is obeyed between 0.08 and 1 ppm of silver. The molar ratio of Ag∶reagent in the separated complex is 1∶2. The effect of foreign ions has been determined and the proposed method can be applied to determination of silver in an exhausted photographic developing solution.

Spectrophotometric extractive determination of thiolactams with picric acid and silver

Spectrophotometric Extractive Determination of Thiolactams with Picric Acid and Silver The thiolactams (Tpl, Tpr, Tkl, Tel) form with Ag+ and picric acid in solutions a complex with a molar ratio of Ag∶TL∶picric acid=1:1:1, which can be extracted into chloroform. The composition of the solid complexes of thiolactam is 1∶2∶1 (Ag∶TL∶R). The formation of ternary complexes was used in the spectrophotometric determination of thiolactams in a concentration range of 0.2–5.0μg/ml. Lactams do not influence the analytical response. The method is applicable to the determination of the thiolactams in a mixture of caprolactam and in xylene solutions during their synthesis.

Enumeration of the antigenic determinants of human secretory component (SC) and secretory IgA (sIgA)

The number of antigenic determinants of human SC and sIgA was determined with specific anti-SC antibodies isolated from a pool of two hyperimmunized sheep. The Fab' antibody fragments were prepared and [ 125I]labelled, while pure SC and pure sIgA, isolated from colostrum, were labelled with 131I. The [ 125I]Fab' antibodies were added, in very large molar excess, to the [ 131I]antigens at various ratios. The Fab'—Ag complexes were separated from the antibody excess by gel-filtration. The highest Fab'/Ag molar ratios of the complexes, which correspond to the maximal number of accessible antigenic determinants, were calculated. We found at least 16 sites (16.6 ± 1.36) on free SC while only 12 (12.27 ± 0.51) were located on sIgA. These results confirm the existence of a significant number of hidden determinants of the SC subunit of sIgA and establish that about 1 4 of the SC molecule is implied in this binding.

Fractionation of mouse DNA in preparative Ag +-Cs 2SO 4 gradients

The behavior of nuclear mouse DNA in preparative Ag +-Cs 2SO 4 gradients was investigated. Complexing DNA with Ag + at pH 8.8 resulted in a marked increase in mainband buoyant density, unaccompanied by an increase in satellite DNA buoyant density at low molar ratios of Ag + to DNA-P . At higher molar ratios the buoyant density of satellite DNA increased more rapidly than that of mainband DNA so that the two DNA species eventually became inseparable. A plot of buoyant density (ϱ) versus the molar ratio of AG + to DNA-P ( R f ) allowed determination of optimal conditions for separation of mainband DNA from satellite DNA. Combined with density gradient relaxation, the technique allowed separation of milligram quantities of mouse DNA into the two molecular species. The addition of increasing amounts of Ag + also produced a speading of the distribution of mainband DNA (σ), followed by contraction as the amount of silver was further increased. Analysis in neutral CsCl in the analytical ultracentrifuge of samples from various parts of a widely spread distribution showed little, if any, separation on the basis of simple G+C content. Much of the behavior of mouse DNA in these gradients can be explained by postulating two types of silver binding sites: a high affinity site which is absent or present in reduced amount in satellite DNA and a low affinity site which is present in both species. It is suggested that these sites may be related to nucleotide sequence(s).