Dec. 4, 2000 COLLEGE STATION - The discovery of unexpected light emission properties of gold by a Texas A&M University chemist is leading to a wide range of applications in medicine, genetics and chemistry.
John P. Fackler Jr., Distinguished Professor of Chemistry and Toxicology at Texas A&M, discovered six years ago that some gold compounds were emitting fluorescent light in a much longer time than expected.
When a chemical compound is hit by light, it gets excited, and further emits fluorescent light. Fackler discovered that the fluorescent light emitted by some gold compounds could last one million times more than usually observed. "The light must get trapped inside the compound," says Fackler. "Then the light bursts into a glow in longer times than expected."
Fackler noticed that this fluorescence occurs when gold atoms are arranged in chains and the distance between them is 3.5 angstroms (one angstrom is one millionth of a centimeter).
"The gold compound emits fluorescence because gold atoms form linear chains and interact with each other," Fackler says. "The distance between the atoms is very important. If it is over 3.5 angstroms, you do not get fluorescence; if you are below that value, the light changes its color."
The fluorescent light also changes its color depending on the atoms surrounding gold. So different atoms can reveal their presence by the different colors of the fluorescent light emitted by the gold compound.
"These gold compounds have some beautiful capabilities for becoming sensors to detect the presence of small concentrations of components, because light changes its color when gold interacts with different components," Fackler says.
The light emission properties of gold can also be used to detect diseases when gold attaches to nucleic acids in cells.
"As demonstrated by Chad A. Mirkin, professor of chemistry at Northwestern University, gold clusters have been designed to probe nucleic acid structure that might be associated with a particular disease," Fackler says.
One of the most important applications of gold is its use in medical drugs. "In the early 1900s, it was found that gold compounds, particularly gold with sulfur, made people with rheumatoid arthritis feel better," Fackler says. "That led to major efforts to develop drugs that dealt with rheumatoid-like diseases." These drugs originally were introduced in people by injection. About 15 years ago, gold drug pills became available.
"This has been a godsend for a lot of people who can just pop a few pills and get out of bed," Fackler says.
The healing properties of gold in rheumatoid arthritis patients may be due to the way gold interacts with a substance called peroxynitrite, a poison probably produced by the affected cells.
"Peroxynitrite may be the major villain in the deterioration of cells and components of bone that are associated with rheumatoid arthritis. Gold is clearly involved in the production of peroxinitrites, but the details are still under study," Fackler says. Gold drugs are effective for only 25 percent of the patients, however. Many patients develop allergic reactions and other conditions that prevent them from using the drugs.
Gold-based therapy, called chrysotherapy, is also used to cure patients from cancer. Scientists are developing gold drugs to be used in the treatment of prostate cancer.
"The hope is that some of these gold drugs will be as useful in prostate cancers as the platinum drugs are," Fackler says. "To this time, we have not found any that have been as successful as the platinum compounds, but there are still a lot of new compounds that have been generated with gold that may well demonstrate effective properties."
The new gold compounds discovered by Fackler are also used in chemistry. They can act as catalysts, which are intermediaries helping chemical reactions go faster and lead to new chemical products.
"Probably the most exciting applications involving gold follow from the development of brand new catalytic systems," Fackler says.
Besides all the fascination associated with gold as a sign of wealth, gold is now proving to be as fascinating for its many applications.
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