Free Silver Ions Research Articles

Influence of carbon dioxide on the impregnation of the nervous tissue by silver

It has been shown that 4% carbon dioxide (CO2) in the air above reaction mixture inhibits the initiation of the formation of silver nanoparticles from complexes with biogenic amines (noradrenaline and serotonin). At the same concentration of CO2 in the air above solution of AgNO3, which is used for staining nerve tissues by the method of Golgi, neurons are preferentially stained, whereas at a concentration of 0.06%, vessels and poor neurons are stained. It is suggested that the entry of free silver ions to neurons is due to the inhibition of sites of initiation of silver nanoparticles in vessels at high CO2 concentrations, while the lack of inhibition leads to silver precipitation in vessels at low CO2 concentrations. It can be assumed that, for stable silver impregnation, the concentration of CO2 must be controlled.

Cell type-specific responses of peripheral blood mononuclear cells to silver nanoparticles

Silver nanoparticles (Ag-NP) are increasingly used in biomedical applications because of their remarkable antimicrobial activity. In biomedicine, Ag-NP are coated onto or embedded in wound dressings, surgical instruments and bone substitute biomaterials, such as silver-containing calcium phosphate cements. Free Ag-NP and silver ions are released from these coatings or after the degradation of a biomaterial, and may come into close contact with blood cells. Despite the widespread use of Ag-NP as an antimicrobial agent, there is a serious lack of information on the biological effects of Ag-NP on human blood cells. In this study, the uptake of Ag-NP by peripheral monocytes and lymphocytes (T-cells) was analyzed, and the influence of nanosilver on cell biological functions (proliferation, the expression of adhesion molecules, cytokine release and the generation of reactive oxygen species) was studied. After cell culture in the presence of monodispersed Ag-NP (5–30 μg ml −1 silver concentration), agglomerates of nanoparticles were detected within monocytes (CD14+) but not in T-cells (CD3+) by light microscopy, flow cytometry and combined focused ion beam/scanning electron microscopy. The uptake rate of nanoparticles was concentration dependent, and the silver agglomerates were typically found in the cytoplasm. Furthermore, a concentration-dependent activation (e.g. an increased expression of adhesion molecule CD54) of monocytes at Ag-NP concentrations of 10–15 μg ml −1 was observed, and cytotoxicity of Ag-NP-treated monocytes was observed at Ag-NP levels of 25 μg ml −1 and higher. However, no modulation of T-cell proliferation was observed in the presence of Ag-NP. Taken together, our results provide the first evidence for a cell-type-specific uptake of Ag-NP by peripheral blood mononuclear cells (PBMC) and the resultant cellular responses after exposure.

The antibacterial activity of biogenic silver and its mode of action

In a previous study, biogenic silver nanoparticles were produced by Lactobacillus fermentum which served as a matrix preventing aggregation. In this study the antibacterial activity of this biogenic silver was compared to ionic silver and chemically produced nanosilver. The minimal inhibitory concentration (MIC) was tested on Gram-positive and Gram-negative bacteria and was comparable for biogenic silver and ionic silver ranging from 12.5 to 50mg/L. In contrast, chemically produced nanosilver had a much higher MIC of at least 500mg/L, due to aggregation upon application. The minimal bactericidal concentration (MBC) in drinking water varied from 0.1 to 0.5mg/L for biogenic silver and ionic silver, but for chemically produced nanosilver concentrations, up to 12.5mg/L was needed. The presence of salts and organic matter decreased the antimicrobial activity of all types of silver resulting in a higher MBC and a slower inactivation of the bacteria. The mode of action of biogenic silver was mainly attributed to the release of silver ions due to the high concentration of free silver ions measured and the resemblance in performance between biogenic silver and ionic silver. Radical formation by biogenic silver and direct contact were found to contribute little to the antibacterial activity. In conclusion, biogenic nanosilver exhibited equal antimicrobial activity compared to ionic silver and can be a valuable alternative for chemically produced nanosilver.

Nano-silver – a review of available data and knowledge gaps in human and environmental risk assessment

Nano-silver is used in an increasing number of products. Some of the applications have resulted in the concern of governments and the public, since little is known about the potential risks of nano-silver. In this review, an inventory is made to identify knowledge gaps that have to be filled before risks for both man and the environment can be assessed as reliable as for ‘non-nanosized’ chemicals. It is hypothesized that the toxic effects of nano-silver are due to a combination of the specific properties of silver nanoparticles and the generation of ions from them. The main topic for future research is validation of our ‘0-hypothesis’ that toxic effects of nano-silver are proportional to the activity of free silver ions released by the nanoparticles. Furthermore, it must be determined whether – or to what extent – nano-silver particles will enter the body. The outcomes of these tests will determine the requirements for further toxicity testing.

Biofilm control using chlorine-based disinfectants in model drinking water distribution systems

Model distribution systems (annular reactors) were operated to investigate the biofilm disinfection efficacies of three disinfectants: free chlorine, monochloramine and combination of free chlorine and silver ion. Biofilm cell number, coverage and structure were examined. At the same dosages, monochloramine showed the poorest biofilm disinfection efficiency compared to free chlorine and combination of free chlorine and silver ion. 40 μg/l of Ag+ showed positive effect to both two dosages of chlorine (0.5 mg/l and 1 mg/l) to disinfect biofilm bacteria. In addition, combinations of free chlorine and silver ion were found to achieve the highest biofilm coverage reduction, while monochloramine showed the least biofilm removal. Biofilm structure could also be affected by different testing agents.

Conformational Behavior of Giant DNA through Binding with Ag+ and Metallization

The conformational behavior of a long single-chain double-stranded DNA in solutions of free silver ions and silver nanoparticles generated via the reduction of AgNO3 by NaBH4 was monitored by fluorescence and electron microscopies and UV spectroscopy. The interaction of monovalent silver ions with DNA induces shrinking of a DNA-coiled polymer chain as a result of a decrease in the DNA persistence length through the complexation of Ag+ with DNA bases. In contrast, the reduction of silver ions by NaBH4 in DNA solutions triggers DNA compaction: a DNA transition from elongated coil state into a compact state. This transition is continuous, unlike the all-or-none discrete DNA compaction that is commonly seen with multications. It is suggested that the collapse of DNA is accompanied by growth aggregation of silver nanoparticles generated on the DNA template.

Determination of total silver and silver species in coastal seawater by inductively-coupled plasma mass spectrometry after batch sorption experiments with Chelex-100 resin

Sorption experiments in batch mode with Chelex-100 resin have been carried out for the determination of total Ag, labile and inert fractions in seawater from Ria de Vigo (NE Atlantic ocean) by inductively coupled plasma-mass spectrometry (ICP-MS). The method allows an accurate determination of the total Ag thus avoiding the effect of the saline matrix when direct determination by ICP-MS is performed. Similarly, the distribution patterns of Ag among species with different lability can be established in seawater as a function of pH. Species distribution and total Ag contents have been obtained in CRM CASS-4 (near shore seawater) and four coastal seawater samples. While the free silver ion concentration accounts for a significant fraction at low pH, the labile inorganic fraction is most important at natural pH (≈8) in non-polluted seawater. The inert and labile organic fractions were the most relevant in polluted coastal seawater. Complexation mechanisms of silver were also investigated from the sorption curves of silver on Chelex-100 according to the Gibbs-Donnan model. Two complexes were formed, AgL and AgL2 with the following intrinsic complexation constants log β(1np) = −2.11 and −10.02, respectively. The formation of the complex AgL predominates up to pH 4 but is negligible due to chloride ions effect, while the complex AgL2 predominates from pH 4.

Does pre-treatment with lamivudine prime for adefovir resistance of hepatitis B virus infection?

My recent leading article on silver-based products as antimicrobial agents was intended primarily to address microbiological issues such as bacterial susceptibility and the potential for the development of resistance to these products. Consequently, I did not consider the toxicological issues raised by Bayston et al. in their comment upon my article. Obviously, a heavy-metal cation such as silver has the potential to inhibit processes in mammalian cells and as noted by Bayston et al., various forms of silver-associated toxicity have been reported, although fortunately they are rare in clinical practice. Experience with antibiotics tells us that dosing with sub-MIC levels creates conditions favourable for the selection of resistant organisms. Applying these principles to the silver situation led me to conclude that products releasing high levels of silver were unlikely to generate conditions for the selection of silver-resistant microorganisms. However, I agree with Bayston et al. that the use of such products could pose a greater risk of toxicity than low silver release formulations and that the therapeutic index for silver-based products may be rather low. Concerning the issue of zones of inhibition raised by Bayston et al., it may well be true that free silver ions capable of diffusion are not released from nanoparticle systems. Unfortunately, the abstract, cited by Bayston et al., does not appear to support this claim. No zones of microbial inhibition were observed with the silver-impregnated catheters used by the authors, implying no diffusion of free silver ions from the catheter material. However, there appeared to be insufficient silver in this product even to affect the viability of bacteria (Staphylococcus epidermidis) bound to the catheter surface. Consequently, it is difficult for Bayston et al. to argue from these data that organisms attached to the surface of the catheter can be killed by silver in the absence of diffusion of the cation from the device.

Novel composite membranes comprising silver salts physically dispersed in poly(ethylene-co-propylene) for the separation of propylene/propane

Novel composite membranes, which delivered high separation performance for propylene/propane mixtures, were developed by coating inert poly(ethylene-co-propylene) rubber (EPR) onto a porous polyester substrate, followed by the physical distribution of AgBF4. Scanning electron microscopy-wavelength dispersive spectrometer (SEM-WDS) revealed that silver salts were uniformly distributed in the EPR layer. The physical dispersion of the silver salts in the inert polymer matrix, without specific interaction, was characterized by FT-IR and FT-Raman spectroscopy. The high separation performance was presumed to stem from thein-situ dissolution of crystalline silver ionic aggregates into free silver ions, which acted as an active propylene carrier within a propylene environment, leading to facilitated propylene transport through the membranes. The membranes were functional at all silver loading levels, exhibiting an unusually low threshold carrier concentration (less than 0.06 of silver weight fraction). The separation properties of these membranes, i.e. the mixed gas selectivity of propylene/propane ~55 and mixed gas permeance ~7 GPU, were stable for several days.

Reduction of chloride matrix effect using silver oxide as a precipitating reagent for the determination of trace anions in chloride‐rich samples via ion chromatography

A new method was developed for the determination of trace anions in chloride-rich samples via ion chromatography by reducing the concentration of chloride ions using silver oxide as a precipitating reagent. In this method the sample pretreatment was started with the addition of silver oxide powder followed by 8 min of stirring and 2 min of centrifugation at a speed of 1500 rpm. The supernatant was diluted with a 1:10 ratio using deionized water and filtered with a 0.22 microm NC filter. All the samples were analyzed in a Dionex ICS-2500 system with an ED50 electrochemical detector in conductivity mode. On the basis of Dionex IonPac AG18 (50 mm x 2 mm) and AS18 (250 mm x 2 mm) columns, 25 AL sample filtrate was eluted isocratically with a mobile phase of 32 mmol/L NaOH at a flow rate of 0.25 mL/ min and each eluted analyte was detected after postcolumn suppression via a Dionex anion suppressor ULTRA II (2 mm). With this method most of the common anions at mg/kg level in chloride-rich samples can be accurately quantified. By controlling the equivalent weight ratio of silver oxide to chloride in sample solutions and the time of pretreatment, the free silver and chloride ions in the sample solution are optimized such that most coexisting common anions can be determined simultaneously.

Effect of the polymer matrix on the formation of silver nanoparticles in polymer–silver salt complex membranes

AbstractWhen polymer–silver salt complex membranes were exposed to UV irradiation, the separation performances of both the permeance and selectivity for propylene–propane decreased, which was primarily attributed to the reduction of the silver ions in the membranes to silver nanoparticles. Here, the effect of the polymer matrix on the formation of silver nanoparticles in the polymer–silver salt complex membranes was investigated. This effect was assessed for the complexes of two kinds of silver salts (AgBF4 and AgCF3SO3) with several polymeric ligands containing three different carbonyl groups, including poly(vinyl pyrrolidone) (PVP) with an amide group, poly(vinyl methyl ketone) (PVMK) with a ketone group, and poly(methyl methacrylate) (PMMA) with an ester group. UV–vis spectra and transmission electron microscopy (TEM) images clearly indicated that the reduction rate of the silver ions has the following order in the various polymer matrices: PVP > PVMK > PMMA, whereas the size and the distribution of the nanoparticles exhibited the reverse order. The tendency to form silver nanoparticles was explained in terms of the differences between the comparative strengths of the interactions of the silver ions with the different carbonyl oxygens in the matrices, as well as that of the silver ions with counteranions, which was characterized by X‐ray photoelectron spectroscopy (XPS) and FT‐Raman spectroscopy. It was concluded that when the concentration of free silver ions was low due to weak polymer–silver ion and strong silver ion–anion interactions, as found with PMMA, the reduction rate of silver ions to silver nanoparticles was slow. Therefore, the PMMA–silver complex membranes were less sensitive to decreases in separation performance upon UV irradiation than compared to the PVP membranes. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 1168–1178, 2006

Precipitation of Silver Powders in the Presence of Ethylenediamine Tetraacetic Acid

Silver powders can be produced by the reduction of a silver salt in an aqueous solution. The manipulation of the rates of the reaction allows the control of the properties such as size and size distribution of the produced particles. In the present work, we studied the addition of ethylenediamine tetraacetic acid (EDTA) as a complexation agent to moderate the rate of the reduction of silver cations with hydrazine as the reducing agent. The experiments were carried out in a batch reactor at different concentrations of the reactants. In the absence of EDTA, the reaction between hydrazine and the silver cations is extremely fast. It was found that, in the absence of seeds, the reaction starts by the precipitation of the free silver ions followed by a period where any reduced elemental silver forms sub-micrometer particles by nucleation. The addition of seeds promotes the growth of particles and suppresses nucleation. When the concentration seeds are greater than 5.4 x 10 -1 mM, no nucleation is apparent. This allows the determination of the reaction rate between hydrazine and silver cations. At 20 °C, the empirical rate law for the reduction of silver was r Ag = 9.35 [Ag] 1.3 [N 2 H 4 ] 0.7 [EDTA] -1.1 in mmol of Ag/L-min.

Silver based wound dressings and topical agents for treating diabetic foot ulcers

Foot ulceration affects 15-20% of people with diabetes. It is a major precursor to amputation in this patient group, and early and appropriate treatment provides the greatest opportunity for healing. The use of silver for its antimicrobial properties has re-emerged, and modern wound dressings that release a sustained amount of free silver ions, are now widely used in wound management. To evaluate the effects of silver-containing dressings and topical agents on infection rates and healing of diabetes related foot ulcers. Searches were made of the Cochrane Wounds Group Specialised Register (August 2005), the Cochrane Central Register of Controlled Trials (CENTRAL, The Cochrane Library Issue 3 2005) MEDLINE (1966 to October week 2 2004), EMBASE (1980 to October week 2 2004) and CINAHL (1982 to October week 2 2004). The Journal of Wound Care (Volume 12/13 Issues 1-10) was hand-searched. Manufacturers, researchers and local and international wound groups were contacted in order to identify unpublished trials. Web sites for wound groups and World Wide Wounds (www.worldwidewounds.com) were searched. Randomised controlled trials and non-randomised controlled clinical trials were considered for inclusion. Studies were included if they involved participants with Type 1 or Type 2 diabetes and related foot ulcers, met the requirements for randomisation, allocation and concealment where appropriate, and compared the intervention with a placebo or a sham dressing, an alternative non silver based dressing or no dressing, and reported outcomes that represent healing rate or infection. Two authors independently evaluated the papers identified by the search strategy against the inclusion criteria but identified no trials eligible for inclusion in the review. It was not possible to perform planned subgroup and sensitivity analysis in the absence of data. In future, if eligible trials become available, a random effects model will be applied for meta-analysis in the presence of statistical heterogeneity (estimated using the I(2) statistic). Dichotomous outcomes will be reported as risk ratios with 95% confidence intervals (CI), and continuous outcomes as weighted mean differences (WMD) with 95% CI. Statistical significance will be set at P value < 0.05 for all outcomes and the magnitude of the effect will be estimated by calculating the number needed to treat (NNT) with 95% CI. No studies were identified that met with the inclusion criteria Despite the widespread use of dressings and topical agents containing silver for the treatment of diabetic foot ulcers, no randomised trials or controlled clinical trials exist that evaluate their clinical effectiveness. Trials are needed to determine clinical and cost-effectiveness and long term outcomes including adverse events.

The use of Silver-coated Ceramic Beads for Sterilization of Sphingomonas sp. in Drinking Mineral Water

It has been established that certain heavy metals including silver have antibacterial properties, and that they may be useful components of antibacterial materials. This knowledge of the antibacterial activity of silver has already been put to use to decrease the occurrence of urinary catheter infections and to develop topical antibacterial agents for burn victims. In this study, the ability of silver-coated ceramic beads (Ag-CBs), sintered at 375, 400, 425, or 450 °C, to sterilize Sphingomonas sp. in commercial mineral water was evaluated. Over 3% (w/v) Ag-CBs in mineral water completely sterilized Sphingomonas sp. after 6 h, regardless of the sintering temperature. The Ag-CBs sintered at 400 °C were the most useful since they did not produce clouding in the water and the bacteria were effectively killed. The antimicrobial activity of the 400 °C-sintered Ag-CBs was comparable to that of free silver ions at 15 μg/l, showing that the silver ions released from the Ag-CBs resulted in the complete sterilization of the microbial cells in mineral water. These results suggest that Ag-CBs present an easy-to-use option for mineral water sterilization.

Radiolysis of silver ion solutions in ethylene glycol: solvated electron and radical scavenging yields

The solvated electron yield in neat ethylene glycol (1,2-ethanediol), measured using pulse radiolysis, is G ( e solv - ) 10 ns =(1.7±0.2)×10 −7 mol J −1. The rate constant of the reaction of solvated electrons with silver cations is k ( e solv - + Ag + ) =(2.8±0.1)×10 9 dm 3 mol −1 s −1 and the absorption band maximum of Ag 0 is at 350 nm. The surface plasmon band of the silver clusters appears slowly at around 400 nm with a coalescence cascade rate constant of 2×10 6 dm 3 mol −1 s −1. The free silver ions do not scavenge ethylene glycol radicals. In contrast, the γ-radiolysis reduction yield of Ag + into clusters is dose-dependent, changing from G i(Ag n )=(2.5±0.5)×10 −7 mol J −1 at low dose to G max(Ag n )=(7.5±0.5)×10 −7 mol J −1 at higher doses, when clusters accumulate. Silver cations adsorbed on clusters are able to scavenge the ethylene glycol radicals, which also contribute to their reduction for a part of G rad=(5.8±0.5)×10 −7 mol J −1. Considering the different ways the reducing radicals can be produced, it is concluded that they originate from the electron–cation recombination and from the cation–ethylene glycol reaction, but that the dissociation of excited states is a negligible path. The formation mechanisms of the radicals and the rate constants in ethylene glycol are compared with those in water and methanol.

Anomaly and correlation of killing in the therapeutic properties of silver (I) chelation with glutamic and tartaric acids.

To investigate whether silver chelates or silver ions are more effective as therapeutic agents, and to examine their mode of action so that safer and stable compounds that have a broad spectrum of therapeutic activities can be developed. Efficacy was investigated against Pseudomonas aeruginosa (ATCC 15442) by determining MIC via a broth macrodilution procedure using NCCLS methods for antibiotic susceptibility testing. It was found that the responsible agent for silver therapeutic properties is the silver chelates rather than silver ions, contradicting previous findings, and the efficacy profiles mimic that of free silver ions present in solution. Silver therapeutic activities seem to be more effective as complexes-an intracellular package-rather than free silver ions, demonstrating that the effect of silver is linked to cells' DNA unwinding, and not respiratory or membrane functionality as was traditionally recognized.

Analysis of the Complexation Reaction between Ag+ and Ethylene

In the present work the reversible, bimolecular (1,1) reaction between ethylene and Ag+ in concentrated AgNO3(aq) solutions is analyzed. Due to interactions between the positively charged Ag+ ions and the negatively charged NO3- ions, the silver nitrate is not completely dissociated and the actual free silver ion concentration is considerably lower than the maximum theoretical concentration. Especially at low temperatures and high salt concentrations the reduction in the degree of dissociation is significant. The influence of this degree of dissociation of the silver salt is considered and incorporated in the interpretation of the experimentally obtained results. Physical-chemical characteristics, transport properties of the system, the equilibrium constant of complexation, and the order of magnitude of the kinetic constants of the reaction between Ag+ and ethylene are determined. Subsequent calculation of the enhancement factor shows that the actual enhancement factor is almost equal to the infinite enhancement factor, indicating that the complexation reaction is almost instantaneous. The process is diffusion limited and strongly enhanced by the chemical complexation reaction.

Novel silver-containing supramolecular frameworks constructed by combination of coordination bonds and supramolecular interactions.

The hydrothermal reactions of AgNO(3), 4,4'-bipy, and carboxylate ligands gave rise to three supramolecular architectures, namely [Ag(bipy)].H(2)SIPA.1/2bipy.H(2)O (1), [Ag(bipy)].1/2H(2)btec.H(2)O (2), and [Ag(bipy)](2).H(2)dpstc.2H(2)O (3) (H(3)SIPA = 5-sulfoisophthalic acid, bipy = 4,4'-bipyridine, H(4)btec = 1,2,4,5-benzenetetracarboxylic acid, H(4)dpstc = 3,3',4,4'-tetracarboxydiphenyl sulfone). All complexes are extended from Ag-bipy linear chains by the combination of coordination bonds and supramolecular interactions in two different approaches. Complexes 1 and 3 comprise two-dimensional frameworks. In the two complexes, a one-dimensional ladderlike structure is first formed by the connection of a Ag-bipy chain through hydrogen bonding between a free carboxylate/bipy ligand and weak coordinative interactions between a free carboxylate ligand and silver ion. The ladderlike structure is then extended to a two-dimensional layer architecture by pi...pi interactions between bipy ligands of the Ag-bipy chains. Complex 2 possesses a three-dimensional framework. The free H(2)btec(2)(-) ligands form a two-dimensional layer network by hydrogen-bonding interactions between protonated and deprotonated carboxylate groups; meanwhile, pi.pi interactions between bipy ligands of Ag-bipy chains also result in a two-dimensional layer. The two layers are further connected by weak Ag-O interactions to generate a three-dimensional supramolecular structure.

Strip thick-film silver ion-selective electrodes

Miniaturized, planar silver ion-selective electrodes based on thick film of silver sulfide are described. The sensors were fabricated entirely by screen-printing, using low-temperature-curing polymer pastes and polyester substrate in form of flexible foils. Application of the thick-film technology results in highly reproducible and economic fabrication of the electrodes. These strip sensors exhibit analytical characteristics comparable with those for conventional ion-selective electrodes. The electrodes enable fast and reproducible potentiometric measurements with near-nernstian sensitivity. The sensors exhibit low detection limit and therefore, are useful as indicating electrodes in argentometric titrations as well as sensors for free silver ions in complexing media. The electrodes are also useful for determination of silver cations as well as halide anions under flow injection analysis regime.

Mechanism for the Formation of Flake Silver Powder Synthesized by Chemical Reduction in Ethylene Glycol

The chemical reduction process has been used for the synthesis of silver powder in ethylene glycol. The mechanism for the formation of flake powder has been proposed on the basis of analysis of the main factors influencing the morphology of silver powder. The results showed that the key factor for the formation of flake silver powder was the heterogeneous seeds of platinum firstly reduced. It offered a plane for precipitation and reduction of silver later. The concentration of free silver ion was controlled by polyvinyl pyrrolidone (PVP) by the formation of complex. And more PVP was absorbed on the surface of silver ion selectively. Thus the nucleation and growth of silver was influenced and flake silver powder formed.