A report published in the July 8 issue of the journal Proceedings of the National Academy of Sciences (PNAS) is the first to describe the principles behind the stability and electronic properties of tiny nanoclusters of metallic gold. The study, which confirms the "divide and protect" bonding structure, resulted from the work of researchers at four universities on two continents.
"While gold nanoparticles are being used by so many researchers chemists, materials scientists and biomedical engineers no one understood their molecular and electronic structures until now," said Robert Whetten, a professor in the Georgia Institute of Technology's School of Physics and School of Chemistry and Biochemistry. "This research opens a new window for nanoparticle chemistry."
Gold and sulfur atoms tend to aggregate in specific numbers and highly symmetrical geometries. Sometimes these clusters are called "superatoms" because they can mimic the chemistry of single atoms of a completely different element.
Researchers commonly use gold nanoparticles because they are stable and exhibit distinct optical, electronic, electrochemical and bio-labeling properties. However, understanding the physicochemical properties of such clusters is a challenge, according to Whetten, because that requires knowledge of their atomic structures.
A significant advance came in late 2007 though, when Stanford University researchers reported the first-ever total structure determination of a 102-atom gold cluster. The X-ray structure study revealed that pairs of organic sulfur ("thiolate") groups extracted gold atoms from the gold layer to form a linear thiolate-gold-thiolate bridge while interacting weakly with the metal surface below. These goldthiolate complexes formed a sort of protective crust around the nanoparticles.
"This discovery contradicted what most chemists believed was going on which was that the sulfur atom merely sat a
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Georgia Institute of Technology Research News