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Gold is characterized by high density, high electrical and thermal conductivities, and high ductility. At least 26 unstable gold isotopes have been made. Gold is the most noble of the noble metals. Other than in the atomic state, the metal does not react with oxygen, sulfur, or selenium at any temperature. It does, however, react with tellurium at elevated temperatures to produce gold ditelluride which is also found in the naturally occurring mineral, calaverite. Gold reacts with the halogens, particularly in the presence of moisture. Gold reacts with various oxidizing agents at ambient temperatures provided a good ligand is present to lower the redox potential below that of water. Thus, gold is not attacked by most acids under ordinary conditions and is stable in basic media. Gold does, however, dissolve readily aqua regia and in alkaline cyanide solutions in the presence of air or hydrogen peroxide to form (Au(CN) 2 ) − . These reactions are important to the extraction and refining of the metal. Gold is very corrosion and tarnish resistant and imparts corrosion resistance to most of the commonly used gold alloys. Placer mining is the oldest form of gold mining. The technique is still in use in places where appropriate alluvial or marine deposits exist, such as Alaska, but requires large quantities of water. At present, most gold is obtained either by deep mining, most notably in South Africa, or by open pit mining such as in the United States. In refining precious metal scrap and some concentrates, the gold is converted to HAuCl 4 by treatment with aqua regia. After heating to remove nitrogen oxides, gold is precipitated from solution by reduction with sulfur dioxide or ferrous sulfate. Gold is widely distributed and the average content in the earth's crust is estimated to be 3.5 ppb. The gold content of ocean water varies considerably with location. The average value is of the order of 10 ppt, which is well below the concentration (3 ppm) required for economic recovery. Chrysotherapy, therapy with gold compounds, remains as one of the few treatments capable of slowing or halting the damage caused by rheumatoid arthritis. Besides its use for monetary reserves, gold is used in the private sector principally for investment and fabrication. By far, the largest commercial use is jewelry. In the electronics industry, gold is used as fine wires or thin film coatings and frequently in the form of alloys to economize on gold consumption and to impart properties such as hardness. In dentistry, gold is used for a variety of restorations. The chemistry of nonmetallic gold is predominantly that of Au(I) and Au(III) compounds and complexes. Common gold compounds include halides, cyanides, oxides and hydroxides hydroxide, Au(OH) 3 ), and sulfides. Both alkyl and aryl complexes of Au(I) and Au(III) as well as olefin and acetylene complexes have been prepared and studied. An increasing amount of interest has developed in gold‐containing bimetallic cluster compounds.
Gold is characterized by high density, high electrical and thermal conductivities, and high ductility. At least 26 unstable gold isotopes have been made. Gold is the most noble of the noble metals. Other than in the atomic state, the metal does not react with oxygen, sulfur, or selenium at any temperature. It does, however, react with tellurium at elevated temperatures to produce gold ditelluride which is also found in the naturally occurring mineral, calaverite. Gold reacts with the halogens, particularly in the presence of moisture. Gold reacts with various oxidizing agents at ambient temperatures provided a good ligand is present to lower the redox potential below that of water. Thus, gold is not attacked by most acids under ordinary conditions and is stable in basic media. Gold does, however, dissolve readily aqua regia and in alkaline cyanide solutions in the presence of air or hydrogen peroxide to form (Au(CN) 2 ) − . These reactions are important to the extraction and refining of the metal. Gold is very corrosion and tarnish resistant and imparts corrosion resistance to most of the commonly used gold alloys. Placer mining is the oldest form of gold mining. The technique is still in use in places where appropriate alluvial or marine deposits exist, such as Alaska, but requires large quantities of water. At present, most gold is obtained either by deep mining, most notably in South Africa, or by open pit mining such as in the United States. In refining precious metal scrap and some concentrates, the gold is converted to HAuCl 4 by treatment with aqua regia. After heating to remove nitrogen oxides, gold is precipitated from solution by reduction with sulfur dioxide or ferrous sulfate. Gold is widely distributed and the average content in the earth's crust is estimated to be 3.5 ppb. The gold content of ocean water varies considerably with location. The average value is of the order of 10 ppt, which is well below the concentration (3 ppm) required for economic recovery. Chrysotherapy, therapy with gold compounds, remains as one of the few treatments capable of slowing or halting the damage caused by rheumatoid arthritis. Besides its use for monetary reserves, gold is used in the private sector principally for investment and fabrication. By far, the largest commercial use is jewelry. In the electronics industry, gold is used as fine wires or thin film coatings and frequently in the form of alloys to economize on gold consumption and to impart properties such as hardness. In dentistry, gold is used for a variety of restorations. The chemistry of nonmetallic gold is predominantly that of Au(I) and Au(III) compounds and complexes. Common gold compounds include halides, cyanides, oxides and hydroxides hydroxide, Au(OH) 3 ), and sulfides. Both alkyl and aryl complexes of Au(I) and Au(III) as well as olefin and acetylene complexes have been prepared and studied. An increasing amount of interest has developed in gold‐containing bimetallic cluster compounds.
SynopsisThe nature of interaction of Au(II1) with nucleic acids was studied by using methods such as uv and ir spectrophotometry, viscometry, pH titrations, and melting-temperature measurements. Au(II1) is found to interact slowly with nucleic acids over a period of several hours. The uv spectra of native calf-thymus DNA (pH 5.6 acetate buffer containing 0.01M NaC104) showed a shift in X max to high wavelengths and an increase in optical density at 260 nm. There was a fourfold decrease in viscosity (expressed as 7jgp/c). The reaction was faster a t pH 4.0 and also with denatured DNA (pH 5.6) and whole yeast RNA (pH 5.6). The order of preference of Au(II1) (as deduced from the time of completion of reaction) for the nucleic acids in RNA > denatured DNA > DNA. The reaction was found to be completely reversible with respect to KCN. Infrared spectra of DNA-Au(II1) complexes showed binding to both the phosphate and bases of DNA. The same conclusions were also arrived a t by meltingtemperature studies of Au(II1)-DNA system. pH titrations showed liberation of two hydroxyl ions at r = 0.12 [r = moles of HAuC14 added per mole of DNA-(P)] and one hydrogen ion a t r = 0.5. The probable binding sites could be N(1)/N(7) of adenine, N(7) and/or C(6)O of guanine, N(3) of cytosine and N(3) of thymine. The results indicate that Au(II1) ions probably bind to the phosphate group in the initial stages of the reaction, particularly a t low values of r , and participation of the base interaction takes place with time. As the value of r increases, participation of the base interaction also increases. Cross-linking of the two strands by Au(II1) may take place, but a complete collapse of the double helix is not envisaged. It is probable that tilting of the bases or rotation of the bases around the glucosidic bond, resulting in a significant distortion of the double helix, might take place due to binding of Au(II1) to DNA.
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