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Brookhaven Spotlights: News From the March 2003 American Chemical Society Meeting
NOTE TO EDITORS: "Brookhaven Spotlights" is issued periodically to bring you up to date on some of the latest newsworthy developments at the U.S. Department of Energy's Brookhaven National Laboratory. The selected briefings below describe research that Brookhaven scientists will present at the 225th American Chemical Society meeting to be held March 23-27, 2003, in New Orleans, Louisiana. All presentations are in the Ernest N. Morial Convention Center.
Microbeam Radiation Therapy
(Monday, March 24, 9:45 a.m., room 390, as part of a symposium honoring nuclear chemist Demetrios G. Sarantites with the 2003 Glenn T. Seaborg Award)
Despite considerable recent progress in radiation therapy, radiation treatment of brain tumors is often associated with side effects due to damage to normal brain tissue. But scientists working at the National Synchrotron Light Source at Brookhaven Lab are developing a promising radiation therapy technique that is effective in destroying tumors in animal models while sparing normal tissues.
Called microbeam radiation therapy (MRT), this technique, which uses parallel, microscopically thin slices of synchrotron-generated x-rays, preferentially kills tumors in part by acting on blood vessels.
"The way it probably works," says Avraham Dilmanian, MRT's principal investigator and a member of the team that developed the therapy, "is that the endothelial cells, which line the inner walls of blood vessels, survive in the regions between the microbeams, so they can replace the endothelial cells killed by the microbeams. But this repair process somehow fails in the tumor's capillaries because they are very different from those of normal tissues. So, as the tumor's capillaries are destroyed, they cannot feed the tumor anymore, and it eventually dies."
The therapy has not yet been tested in humans and is years away from clinical application, but Dilmanian's results are encouraging. "MRT has proven highly effective in the treatment of certain experimental rat brain tumors, with minimal impact on adjacent normal brain tissue," he says. "Our results support the idea that MRT could offer control of brain cancer with fewer deleterious side effects."
Two Steps Are Better Than One
(Monday, March 24, 10:50 a.m., room 283)
Brookhaven chemist Hua-Gen Yu has devised a new way to speed up computer calculations of how molecules with up to six atoms rotate and vibrate, providing new insights into the structure of greenhouse gases and the inner workings of combustion reactions. The method, called two-layer Lanczos algorithm, is a modified version of a well-known method introduced in 1956, and has been successfully applied to methane, formaldehyde and rare-gas molecules, which are compounds containing rare-gas atoms.
"This new algorithm is not only faster than other methods, but it also reduces the amount of required computer memory," Yu says. "So these features make it feasible to study molecules with five or more atoms by using a rigorous theory."
To determine the rotational and vibrational energies of a molecule, chemists collect information about the positions of its atoms in space from a matrix, which is a table of numbers. The bigger the molecules, the larger the matrix and the longer it takes for a computer to extract information about the rotational and vibrational states of the molecule.
"The reason the two-layer Lanczos method is more efficient than other methods is that it divides the original matrix into two smaller ones," Yu explains, "which are each solved by a standard method."
The scientists have applied the method to formaldehyde, confirming previous results, but their calculations were performed in 2.5 hours, or ten times faster than by using standard methods.
Probing Electron Transfer Between Molecules
(Monday, March 24, 2:00 p.m., room 298)
To be able to build electronic devices- such as switches and transistors - out of molecular materials, scientists need to know how electrons are transferred between molecules. "Scientists have long recognized that single molecules might very well be made to perform the basic functions of electronic circuit elements," says Brookhaven Lab theoretical chemist Marshall Newton. "So we need to know how to control the flow of electrons between molecules."
Newton and his experimental colleagues John Smalley and Stephen Feldberg created small devices, each composed of a gold electrode, a bridge, and acceptor molecules made of either ferrocene or ruthenium.
By looking at how electrons are transferred between the electrode and the molecular acceptors, the scientists were surprised to notice that the speed of the electrons inside the bridge reached a limit for small bridges.
Newton suggests that two phenomena might cause this limiting behavior: defects in the molecular conformation of the bridge might decrease the coupling of the acceptor to the electrode, or the self-assembled film which supports the bridge might reorganize itself.
"Nanometer-sized molecular structures are made of 'bundles' of molecules, so it is challenging to understand how electrons move around them," Newton says. "What we have found shows that we still need a better understanding of electron transport before we can construct the basic circuit elements needed for a molecular electronic device."
Combining Techniques to Peer at Chemical Reactions
(Tuesday, March 25, 9:50 am, room 227)
To obtain a detailed picture of chemical reactions involving hydrocarbons, a team of scientists led by Brookhaven Lab chemist Arthur Suits has combined a method using lasers and molecular beams, called a crossed molecular beam method, with a successful imaging technique that determines the velocity of the reaction products.
"The crossed molecular beam method is the most powerful means of obtaining detailed insight into elementary reaction dynamics, and imaging methods have achieved tremendous advances in velocity resolution," Suits says. "So we have combined both methods to explore the detailed dynamics of the reactions of oxygen with alkanes, which are hydrocarbons such as natural gas and fossil fuels."
By using this approach, Suits and his colleagues made unexpected observations. For example, by comparing the dynamics of the reaction when using excited and non-excited oxygen atoms, they noticed that the products were spatially distributed in two different ways. "The results show dramatically contrasting dynamics," Suits says, "with backward-sideways scattering dominating the reaction with non-excited oxygen and forward scattering for the reaction with excited oxygen. In both cases, the products are highly excited - more so than previously believed."
The researchers also tried to detect a product called hydroxymethyl, which was thought to be produced in the reaction between excited oxygen and methane, but they saw no evidence for hydroxymethyl. "It may well be that the bulk of the hydroxymethyl radical products undergo secondary decomposition, a process that seems to have been neglected in previous studies," Suits explains.
Running as Fast as Radicals
(Thursday, March 27, 10:50 a.m.)
A team of scientists led by Brookhaven Lab chemist Christopher Fockenberg has constructed an apparatus that can detect the products of chemical reactions as they are formed. These reactions involve radicals, which are highly reactive molecules present in the combustion of fossil fuels.
"Reactions between radicals are challenging to study," Fockenberg says, "because they lead to more reactions and products than those expected from the reaction of interest alone. Now, we can detect even 'unexpected' products generated during the reaction with a time resolution never achieved before."
With their apparatus, Fockenberg and his colleagues successfully identified the reactants and products in the reaction of methyl radicals with oxygen atoms. To their surprise, the scientists noticed the formation of not only formaldehyde and hydrogen atoms, but also a significant amount of carbon monoxide with hydrogen molecules and atoms.
The researchers next plan to investigate reactions involving other radicals, which may help scientists devise ways to reduce atmospheric emissions of pollutants.