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Iowa State University researchers, in collaboration with scientists from the University of Michigan, have identified a method for producing gold nanoparticles using a compound made by bacteria.  This method may have utility for the production of thin films or wires, or for delivery of gold as a treatment for rheumatoid arthritis.

Methanobactin is a small peptide secreted by methane-oxidizing or methanotrophic bacteria and binds to extracellular copper when these bacteria are grown under low copper conditions.  Methanobactin is also able to bind to a number of other metals, including gold, iron, nickel, zinc, cobalt, cadmium, mercury, and uranium.  ISU researchers and their collaborators investigating the properties of methanobactin have determined that gold in the 3+ oxidation state, Au(III), can be reduced to its zero oxidation state, Au(0) at or below ratios of one Au(III) per methanobactin molecule.  Under these conditions, the Au(0) remains associated with the methanobactin, and could serve as a soluble delivery/extraction system for the generation of gold thin films or wires by application to surfaces.  Additionally, this methanobactin-Au(III) binding and reduction system may serve as an aurothiolate-type system for the administration of Au(0) for the treatment of rheumatoid arthritis.  At ratios of Au(III) to methanobactin above one to one, methanobactin binds and catalytically reduces Au(III) to Au(0) with the concomitant production of gold nanoparticles, and this approach can also be used for the formation of gold nanoparticles. Continuous reduction of gold by methanobactin can also be achieved if a reductant is provided.  Thus, methanobactin has the potential to replace the use of toxic cyanide for the recovery of gold from ores.

• Versatile (ratio of Au(III) to methanobactin can be varied to produce gold thin films, wires or nanoparticles)

• Stable (at ratios of one or fewer Au(III) per methanobactin, gold remains bound in the Au(0) state, avoiding the toxic effects of gold oxidation of other aurothiolate-type treatments for rheumatoid arthritis)

• Simple (methanobactin can be purified using a one-step procedure and gold can be recovered by centrifugation)

Production of gold or copper nanoparticles, generation of gold thin films or wires; recovery of gold from ores; treatment of rheumatoid arthritis

1: “Spectral and thermodynamic properties of Ag(I), Au(III), Cd(II), Co(II), Fe(III), Hg(II), Mn(II), Pb(II), U(VI), and Zn(II) binding by methanobactin from Methylosinus trichosporium OB3b”, Choi, D. W. et al., 2006, J. Inorg. Biochem. 100:2150-2161.

2: “Spectral, kinetic and thermodynamic properties of Cu(I)- and Cu(II)-binding by methanobactin from Methylosinus trichosporium OB3b”, Choi, D. W. et al., 2006, Biochemistry 45:1142–1153.

3: “Oxidase, superoxide dismutase, and hydrogen peroxide reductase activities of methanobactin from type I and II methanotrophs”, Choi, D.W. et al., 2008, J. Inorg. Biochem. 102:1571–1580.