Silver compounds biology

Silver compounds having anions that are inherently toxic, eg, silver arsenate and silver cyanide, can cause adverse health effects. The reported rat oral LD values for silver nitrate, silver arsenate [13510-44-6] and silver cyanide are 500—800 (29), 200—400 (29), and 123 mg/kg (30), respectively. Silver compounds or complexes ia which the silver ion is not biologically available, eg, silver sulfide and silver thiosulfate complexes, are considered to be without adverse health effects and essentially nontoxic. 

Silver, S. 2003. Bacterial silver resistance Molecular biology and uses and misuses of silver compounds. FEMS Microbiology Reviews, 27 341-53. 

Metallic silver normally consists of Ag (52%) and (48%), although 25 isotopes are known to exist. The radioactive isotopes of silver range from Ag with a half-life of 5 s to Ag with a half-life of 5 years. Silver is almost always monovalent in its compounds, but the oxide, fluoride, and sulfide of divalent Ag are known, as are a few compounds with Ag(III). Ag forms stable coordination complexes with organic groups it has great affinity for thiol, sulfide, and seleno-sulfide, and reacts with amino, carboxyl, and phosphate groups present in biologically active molecules. The Ag" is colorless, but a number of silver compounds are colored because of the influence of other constituents (Table 8.2-1). 

Cobalt compounds have been in use for centuries, notably as pigments ( cobalt blue ) in glass and porcelain (a double silicate of cobalt and potassium) the metal itself has been produced on an industrial scale only during the twentieth century. Cobalt is relatively uncommon but widely distributed it occurs biologically in vitamin B12 (a complex of cobalt(III) in which the cobalt is bonded octahedrally to nitrogen atoms and the carbon atom of a CN group). In its ores, it is usually in combination with sulphur or arsenic, and other metals, notably copper and silver, are often present. Extraction is carried out by a process essentially similar to that used for iron, but is complicate because of the need to remove arsenic and other metals. 

Since the discovery in 1964 that the antibiotic valinomydn exhibited alkali cation specificity in rat liver mitochondria, a new area of research has developed, based not only on biological systems but also on model systems such as crown ethers.484 The ability of neutral compounds to form lipid-soluble alkali and alkaline earth complexes was observed in 1951. The structure of the corresponding ligand, the anion of the antibiotic nigericin (78), was characterized as its silver salt in 1968.488 486 Silver was used as a heavy atom crystaUographically, since the Ag+ cation had a radius between that of Na+ and K+, which were the two alkali cations with which nigericin was most active. 

In fresh water, silver may form complex ions with chlorides, ammonium (in areas of maximum biological activity), and sulfates form soluble organic compounds such as the acetate and the tartrate become adsorbed onto humic complexes and suspended particulates and become incorporated into, or adsorbed onto, aquatic biota (Boyle 1968). Where decaying animal and plant material are abundant, silver strongly precipitates as the sulfide or combines with humic materials (Smith and Carson 1977). 

EPA. 1985b. Silver. Chemical, physical and biological properties of compounds present at hazardous waste sites. Washington, DC US Environmental Protection Agency, Office of Waste Programs and Enforcement. PB89-132203. 

Petering, H. G. and C. J. McClain. 1991. Silver. In E. Merian, Ed. Metals and Their Compounds in the Environment Occurrence, Analysis, and Biological Relevance. VCH Publishers, New York, pp. 1191-1202. 

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