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PubMed2005

Organometallic silver(I) supramolecular complexes generated from multidentate furan-containing symmetric and unsymmetric fulvene ligands and silver(I) salts.

One new conjugated symmetric fulvene ligand L1 and two new unsymmetric fulvene ligands L2 and L3 were synthesized. Five new supramolecular complexes, namely Ag2(L1)3(SO3CF3)3 (1) (1, monoclinic, P2(1)/c; a = 12.702(3) A, b = 26.118(7) A, c = 13.998(4) A, beta = 96.063(4) degrees, Z = 4), [Ag(L1)]ClO4 (2) (monoclinic, C2/c; a = 17.363(2) A, b = 13.2794(18) A, c = 13.4884(18) A, beta = 100.292(2) degrees, Z = 8), [Ag(L1)(C6H6)SbF6] x 0.5C6H6 x H2O (3) (monoclinic, P2(1)/c; a = 6.8839(11) A, b = 20.242(3) A, c = 18.934(3) A, beta = 91.994(3) degrees, Z = 4), Ag(L2)(SO3CF3) (4) (triclinic, P1; a = 8.629(3) A, b = 10.915(3) A, c = 11.178(3) A, alpha = 100.978(4) degrees, beta = 91.994(3) degrees, gamma = 105.652(4) degrees, Z = 2), and Ag(L3)(H2O)(SO3CF3) (5) (triclinic, P1; a = 8.914(5) A, b = 10.809(6) A, c = 11.283(6) A, alpha = 69.255(8) degrees, beta = 87.163(9) degrees, gamma = 84.993(8) degrees, Z = 2) were obtained through self-assembly based on these three new fulvene ligands in a benzene/toluene mixed-solvent system. Compounds 1-5 have been fully characterized by infrared spectroscopy, elemental analysis, and single-crystal X-ray diffraction. The results indicate that the coordination chemistry of new fulvene ligands is versatile. They can adopt either cis- or trans-conformation to bind soft acid Ag(I) ion through not only the terminal -CN and furan functional groups but also the fulvene carbon atoms into organometallic coordination polymers or discrete complexes. In addition, the luminescent properties of L1-L3 and their Ag(I) complexes were investigated preliminarily in EtOH and solid state.

Journal Article↗
PubMed1999

Sound production by abdominal tymbal organs in two moth species: the green silver-line and the scarce silver-line (Noctuoidea: Nolidae: Chloephorinae).

Male moths of the chloephorine species Pseudoips prasinana and Bena bicolorana produce clicks (approximately 100 dB peSPL at 10 cm) using ventral tymbal organs located in a cleft in the second abdominal sternite. Large muscles insert on the dorsal part of the tymbal frame and rhythmically flex a thin sheet of cuticle. Normally, each sound-production cycle contains four clicks, the left and right tymbals producing clicks both on active buckling caused by muscle contraction and on the passive elastic return from buckling. Histochemical staining indicated the presence of elastic resilin-like proteins in the tymbals. Obvious differences between the click patterns of the two species reflect differences in their tymbal morphology. P. prasinana has smooth tymbals and produces a single click (300 µs, 40 kHz) for each tymbal buckling. In contrast, B. bicolorana has striae on the medial part of the tymbals. Accordingly, it produces many clicks per buckling. The click pattern is a heterogeneous mixture of large clicks at 52 kHz, resembling those of P. prasinana, interspersed with series of broad-band clicks (20-100 kHz) of lower intensity (15-20 dB). Thus, in chloephorine moths, there is a correlation between the structure and function of the smooth and striated tymbals that is strikingly similar to that in arctiid moths, although the two types of tymbals have evolved independently. The hearing of P. prasinana is tuned to its own sounds with lowest threshold (38 dB SPL) at 40-60 kHz. We suggest that sound production in male chloephorines plays a part in sexual acoustic communication.

Journal Article↗
PubMed2005

Properties of titanium-silver alloys for dental application.

The purpose of this study was to develop titanium-silver alloys with biocompatibility, high corrosion resistance, and low ion-release rate, and to evaluate the electrochemical properties of titanium-silver alloys in artificial saliva. Titanium-silver alloys with silver contents ranging from 0 to 4.5 at % in steps of 0.5 at % were designed. The alloys were arc melted, homogenized at 950 degrees C for 72 h, hot rolled to 2 mm in thickness, and finally solution heat treated at 950 degrees C for 1 h and quenched in water. Chemical compositions, phases, hardnesses, electrochemical properties, and the cytotoxicity of the alloys were investigated. The purity of titanium-silver alloys was maintained above 99.9%, because few impurities were introduced through their manufacture. In the case of alloys containing silver in the range 2.0-4.0 at %, the formation of an acicular alpha phase was observed inside the beta phase. The acicular phase got thinner with increasing amounts of silver. This means that silver is a beta-phase stabilizing element in titanium-silver alloys. The hardness value tended to rise with increasing silver content and increased largely over 3.5 at %, and the increase of the hardness value versus pure titanium was about 33%. It is believed that the substantial increases in hardness was due to the effects of solid solution strengthening and of alpha-beta phase transition. Moreover, titanium-silver alloys had higher corrosion resistances than pure titanium. These results mean that silver additions to titanium can improve alloy corrosion resistance. Passive current densities in the potentiodynamic polarization curves were dependent on the chemical compositions of the titanium-silver alloys. However, they did not show a linear relationship with respect to silver contents. Titanium-silver alloys did not show pitting corrosion in artificial saliva. It is believed that silver addition to titanium strengthened the passive film due to titanium dissolution induced by the different electromotive forces of titanium and silver. In the agar overlay test, the cytotoxicity of the titanium-silver alloys and of titanium were none or mild. In summary, titanium-silver alloys had higher mechanical properties and corrosion resistance than titanium, and toxicities that were similar to titanium. Therefore, it is recommended that titanium-silver alloys be adopted cautiously by the biomedical and dental fields.

Alloys↗
PubMed2006

Silver in health care: antimicrobial effects and safety in use.

Silver has a long and intriguing history as an antibiotic in human health care. It has been developed for use in water purification, wound care, bone prostheses, reconstructive orthopaedic surgery, cardiac devices, catheters and surgical appliances. Advancing biotechnology has enabled incorporation of ionizable silver into fabrics for clinical use to reduce the risk of nosocomial infections and for personal hygiene. The antimicrobial action of silver or silver compounds is proportional to the bioactive silver ion (Ag(+)) released and its availability to interact with bacterial or fungal cell membranes. Silver metal and inorganic silver compounds ionize in the presence of water, body fluids or tissue exudates. The silver ion is biologically active and readily interacts with proteins, amino acid residues, free anions and receptors on mammalian and eukaryotic cell membranes. Bacterial (and probably fungal) sensitivity to silver is genetically determined and relates to the levels of intracellular silver uptake and its ability to interact and irreversibly denature key enzyme systems. Silver exhibits low toxicity in the human body, and minimal risk is expected due to clinical exposure by inhalation, ingestion, dermal application or through the urological or haematogenous route. Chronic ingestion or inhalation of silver preparations (especially colloidal silver) can lead to deposition of silver metal/silver sulphide particles in the skin (argyria), eye (argyrosis) and other organs. These are not life-threatening conditions but cosmetically undesirable. Silver is absorbed into the human body and enters the systemic circulation as a protein complex to be eliminated by the liver and kidneys. Silver metabolism is modulated by induction and binding to metallothioneins. This complex mitigates the cellular toxicity of silver and contributes to tissue repair. Silver allergy is a known contra-indication for using silver in medical devices or antibiotic textiles.

Administration, Cutaneous↗
PubMed2005

Evaluation of a standardized method for determining soluble silver in workplace air samples.

Several occupational exposure limits and guidelines exist for silver, but the values for each depend on the chemical form of the silver compound in question. In the past, it generally was not possible, without prior knowledge of the work process, to distinguish soluble silver from insoluble silver compounds collected in workplace air samples. Therefore, analytical results were historically reported as total silver. In this study, work was conducted to evaluate a method to differentiate between the quantities of water-soluble silver compounds and total silver collected on filters. The investigation entailed an evaluation of an International Organization for Standardization method to determine soluble silver in airborne particulate matter. The study design incorporated laboratory experiments to evaluate analytical figures of merit, such as selection of appropriate filter media and extraction solution, analytical recovery, and sample stability during storage. Polytetrafluoroethylene (PTFE) filters (2 microm, 37 mm) in opaque cassettes were either spiked with known amounts of silver nitrate or contained a known mass of solid silver nitrate. Results showed that over 90% of the silver was recovered from PTFE filters. Also, field studies were conducted in which workplace air samples were collected in two silver refineries. Some of these samples were analyzed only for soluble silver while others were sequentially extracted and analyzed, first, for soluble silver, then for total silver. The mass fractions of soluble silver, as compared to total silver, were approximately 2% or less. This investigation served to validate an international standard procedure for the determination of soluble silver in workplace air samples.

Air Pollutants, Occupational↗
PubMed2006

A missense mutation in PMEL17 is associated with the Silver coat color in the horse.

BACKGROUND: The Silver coat color, also called Silver dapple, in the horse is characterized by dilution of the black pigment in the hair. This phenotype shows an autosomal dominant inheritance. The effect of the mutation is most visible in the long hairs of the mane and tail, which are diluted to a mixture of white and gray hairs. Herein we describe the identification of the responsible gene and a missense mutation associated with the Silver phenotype. RESULTS: Segregation data on the Silver locus (Z) were obtained within one half-sib family that consisted of a heterozygous Silver colored stallion with 34 offspring and their 29 non-Silver dams. We typed 41 genetic markers well spread over the horse genome, including one single microsatellite marker (TKY284) close to the candidate gene PMEL17 on horse chromosome 6 (ECA6q23). Significant linkage was found between the Silver phenotype and TKY284 (theta = 0, z = 9.0). DNA sequencing of PMEL17 in Silver and non-Silver horses revealed a missense mutation in exon 11 changing the second amino acid in the cytoplasmic region from arginine to cysteine (Arg618Cys). This mutation showed complete association with the Silver phenotype across multiple horse breeds, and was not found among non-Silver horses with one clear exception; a chestnut colored individual that had several Silver offspring when mated to different non-Silver stallions also carried the exon 11 mutation. In total, 64 Silver horses from six breeds and 85 non-Silver horses from 14 breeds were tested for the exon 11 mutation. One additional mutation located in intron 9, only 759 bases from the missense mutation, also showed complete association with the Silver phenotype. However, as one could expect to find several non-causative mutations completely associated with the Silver mutation, we argue that the missense mutation is more likely to be causative. CONCLUSION: The present study shows that PMEL17 causes the Silver coat color in the horse and enable genetic testing for this trait.

Amino Acid Sequence↗
PubMed1985

Biologic monitoring of workers exposed to silver.

The smelting and refining of silver and the preparation of silver salts for use in photosensitized products can lead to occupational exposures to silver. Our objectives in this study were to determine the absorption and elimination of silver by workers exposed to different species of silver, to estimate the body burden of silver and to relate these findings to the potential development of argyria. Workers potentially exposed to silver (n = 37) and a similar number of controls (n = 35) participated in this study. Blood, urine, feces and hair samples were collected and were analyzed for total silver content by atomic absorption spectroscopy. The mean concentration of silver in the blood, urine and feces of silver workers was 0.011 microgram/ml, less than 0.005 microgram/g and 15 microgram/g, respectively; and of controls was less than 0.005 microgram/ml, less than 0.005 microgram/g and 1.5 microgram/g, respectively. The concentration of silver in hair was markedly higher for the silver workers than for controls (130 +/- 160 vs 0.57 +/- 0.56 microgram/g, respectively). The importance of these latter findings was questionable since airborne particles of silver can bind to hair and lead to apparent high values. Since silver is eliminated predominantly in the feces, fecal measurements were used as an index of exposure and as a means of calculating body burdens. Human exposure to metallic silver at the TLV (0.1 mg/m3) is expected to lead to a fecal excretion of about 1 mg of silver per day.(ABSTRACT TRUNCATED AT 250 WORDS)

Absorption↗
PubMed1997

Partitioning and effects of silver in amended freshwater sediments.

Sediments that represented a wide range of characteristics were amended with silver compounds to observe partitioning and bioavailability. In laboratory studies, silver partitioning to particulates, sediment pore water, and overlying water was measured and bioavailability of silver was determined using Hyalella azteca in 10-day sediment toxicity tests. Three silver compounds were used as sources of silver for this study: silver nitrate, silver chloride, and silver thiosulfate complex. Sediment amendment procedures were adjusted as necessary depending on the characteristics of the individual compounds. Several sediment characteristics such as organic carbon, pH, redox, and acid volatile sulfides regulated silver partitioning and bioavailability. Bioavailability of silver was correlated with the overlying water concentration of silver. Ten-day LC50 values ranged from 1.62 to 379.7 mg Ag/kg for H. azteca exposed to sediments amended with AgNO3. In laboratory experiments, silver chloride and silver thiosulfate were orders of magnitude less toxic and bioavailable than silver nitrate, with 10-day LC50 values greater than the highest concentrations of AgCl and silver thiosulfate complex amended to sediments (2560 and 1125 mg Ag/kg, respectively.

Animals↗