Sunday, April 13, 2008
Fullerenes, also fondly known as buckyballs, are showing an ugly side. It appears that the hydrophobic, or water hating, carbon molecules clump together in water, forming aggregates of thousands of molecules. And there are reports that these aggregates can be toxic to microorganisms and even fish, should they escape from processing into surface water and ground water.
Nanotechnology In Environment: Citrate Appears To Control Buckyball Clumping But Environmental Concerns Remain
Fullerenes, also fondly known as buckyballs, are showing an ugly side. Since being discovered in 1985, the hollow carbon atoms have been adapted for nanotechnology and biomedical applications ranging from electronics to carriers of imaging materials.
It appears that the hydrophobic, or water hating, carbon molecules clump together in water, forming aggregates of thousands of molecules. And there are reports that these aggregates can be toxic to microorganisms and even fish, should they escape from processing into surface water and ground water.
Now researchers at Virginia Tech have demonstrated that this behavior can be changed by the addition of citric acid -- although the good news and bad news of this recent discovery has yet to be determined. They recently reported on their research to both environmental chemists and colloidal chemists at the American Chemical Society 235th national meeting.
"Our group and other research groups worldwide are examining what makes these fullerene aggregates tick and how they form," said Peter Vikesland, associate professor of civil and environmental engineering at Virginia Tech. "Once they clump, they don't settle out. People don't know why they remain suspended. And we don't really know how many molecules are in a clump. We use the term nC60 where N means some number that is extremely large."
What Vikesland's group has done that is different and novel is, instead of mixing the molecules with water, they have added citric acid, a naturally occurring and readily available acid. "The result is that instead of unstructured clumps, we get reproducible sphere-shaped aggregates," he said.
They discovered, for example, that in the presence of a little bit of acid, which emulates the environment in the case of an accidental release of fullerenes, the aggregates are similar to those formed in water alone. But when more acid is added, the diameter of the aggregates becomes smaller. "We want to understand the implications of this finding to the toxicity, movement, and fate of fullerenes in the environment."
Citric acid is well understood as a proxy for other kinds of organic acids, including those within cells. Some of the citrate-based spheres that Vikesland's group discovered are similar to what happens intercellularly when human cells are exposed to C60, he said. "We think citrate and other organic acids with a carboxyl group make C60 more water soluble."
Vikesland presented "Effects of small molecular weight acids on C60 aggregate formation and transport (ENVR 26)" to the Division of Environmental Chemistry on April 6. Authors of the paper are Vikesland, civil and environmental engineering Ph.D. student Xiaojun Chang of Luoyang, Henan, China, and master's degree student Laura K. Duncan of Augusta, Ga., and research assistant professor and TEM lab director Joerg R. Jinschek.
Future environmental research will be done with simulated subsurface environments using a sand column to determine how these acidified masses move in ground water.
Vikesland will present Chang's and his research about how C60 and citric acid interact to the Division of Colloid and Surface Chemistry on April 9 at the same conference. He will present the results of various imaging analysis, such as atomic force microscopy. "We have no answers but we have a hypothesis, still unproven, that there are weak interactions between citrate and individual carbon molecules that cause the spherical shape," Vikesland said.
The Vikesland group is exploring whether the C60-citrate interaction can be used to create reproducible shaped objects. Many fullerene-based products presently require solvents, which are then washed off. Unfortunately, the engineered fullerenes can retain solvents. Using citrate "is very green chemistry," Vikesland said. "There are no solvents. It is a cleaner way to produce these things. Citrate may be an alternative."
But there are challenges. "It's not a hard bond but a weak attractive force, which makes these spherical aggregates challenging to work with. At the present time we don't know how they will fall apart and what their products are," Vikesland said.
In the meantime, the solvent issue aside, the current rush to put fullerenes into materials may not be wise "because we don't understand what is going on," said Vikesland. "If you have a face cream with fullerenes as an antioxidant -- we don't know how they will react. There are many organic acids in the environment."
He concludes, "There are uncertainties. Everyone wants to prevent future problems."
Vikesland research is supported by the National Science Foundation. The project was also supported by the Institute for Critical Technology and Applied Science at Virginia Tech.
Posted by SANJIDA AFROJ at 10:45 PM
A screenshot from the University of Washington's Hubble Web site pinpoints "black holes" on the Internet. Green pointers indicate black holes that have lasted less than 8 minutes. Yellow, pink and red pointers highlight Internet addresses that have been inaccessible for longer periods.
Black holes’ charted on the Internet
Messages throughout the world are constantly lost to cyber black holes
You’re pounding the keyboard, double-clicking away, sighing and grumbling, but to no avail: That devilish little hourglass icon refuses to give way to the Web site you’re trying to reach. Most Internet users have encountered trouble reaching online destinations, but they often attribute the problem to their wireless network cutting out or a server momentarily going down.
Sometimes, though, the problem is more mysterious. At any given moment, messages throughout the world are lost to cyber black holes, according to new computer science research.
Ethan Katz-Bassett, a graduate student in computer science at the University of Washington, and his advisor, Arvind Krishnamurthy, designed a program to continuously search for these strange Internet gaps, when a request to visit a Web site or an outgoing e-mail gets lost along a pathway that was known to be working before. To make sure the black holes they detect are not simply due to a problem with the end user or the host server, they look for computers that can be reached from some, but not all, of the Internet, meaning the issue must be occurring en route.
We were astounded when we did an initial four-month study and we saw how many problems there were," Katz-Bassett said. "It seemed infeasible that this could be happening so often. They’re definitely more common than we thought."
Now the team constantly monitors the Web for black holes and posts a map of where the problems are around the world at any given moment. They hope their data will help Internet service providers track down the route of problems experienced on their networks.
"Network administers are definitely interested in it," Katz-Bassett said. "I think we need to do more analysis of the data and see where exactly these problems are occurring. It would be interesting to come up with predictions about where problems were most likely to occur."
The scientists named their monitoring system Hubble after the Hubble Space Telescope, which can also detect black holes, albeit the astrophysical kind. They hope their data will help improve the consistency of the Internet, where we increasingly entrust vital information.
I think we would like it to be more reliable," Katz-Bassett said. "It’s orders of magnitude less reliable than the telephone network right now. I think it should be pretty possible to get it closer."
The researchers will present their findings at the Usenix Symposium on Networked Systems Design and Implementation being held next week in San Francisco. The project was funded by the National Science Foundation.
Posted by SANJIDA AFROJ at 10:28 PM