April 7, 2002
Brookhaven Spotlights: News From the April 2002 American Chemical Society Meeting
Nanocatalysts and Atmospheric Chemistry
Brookhaven chemists have developed computer simulations describing the atomic-level mechanisms of chemical reactions involved in the combustion of hydrocarbon fuels, and the role of chemicals a billionth of a meter in size in speeding up these reactions.
The reaction of hydroxyl radicals – a major cause of smog and
atmospheric pollution – with carbon monoxide to produce carbon dioxide is
poorly understood, despite being the primary mechanism for removal of
carbon monoxide from the atmosphere. When the hydroxyl radical (OH) and
carbon monoxide (CO) combine, they form a transient molecule, HOCO, that
later breaks into carbon dioxide and hydrogen.
Having previously simulated the reaction of OH with CO, chemist James T. Muckerman and research associate Hua-Gen Yu have now simulated how light breaks the bonds between the atoms of the HOCO molecule. They found that when light excites a specific vibrational state of the OH bond, HOCO breaks into both hydroxyl radical and carbon monoxide, and carbon dioxide and hydrogen. The most interesting result, Yu said, is that when light hits the OH bond, it is broken in only one-third of the cases, and the nearby CO bond is split the rest of the time. “This result may seem counter-intuitive,” he said, “but it is due to the fact that the bonds are coupled, and what affects one bond affects its neighbors as well.”
Muckerman said that the new calculation methods for many-atom systems
will be important in studying how nanocatalysts – chemicals the size of a
billionth of a meter – speed up chemical reactions. “Nobody really
understands how nanocatalysts work,” Muckerman said. “So we are now using
our simulations to investigate the role of these catalysts at the atomic
Helping to Fuel Efficient Electric Vehicles
Brookhaven scientists have developed a new method of creating catalysts that could allow the production of cheaper and more efficient fuel cells – highly efficient electrical energy sources that may one day replace cars’ internal combustion engines.
Like a regular battery, a fuel cell produces electricity as a result of chemical reactions. Unlike a battery, however, a fuel cell does not require charging, but instead produces energy by feeding hydrogen and oxygen onto metal-based plates called electrodes. The chemical energy is converted into electrical energy as the electrons flow between the electrodes.
To maximize the chemical reactions inside the fuel cell, both electrodes contain a catalyst, or “electrocatalyst.” One of the most efficient electrocatalysts is made of an alloy of platinum and ruthenium, but its efficiency is reduced by carbon monoxide deposits formed on the platinum as a by-product of the hydrogen-oxygen reaction. The new method developed by the Brookhaven team, led by chemist Radoslav Adzic, reduces the amount of platinum present in the catalyst, thus limiting carbon monoxide accumulation and improving fuel cell performance.
In the new method, platinum atoms are deposited on the surface of tiny
ruthenium crystalline particles. In contrast, typical platinum-ruthenium
alloy catalysts have platinum throughout. “Our method very likely makes
almost all of the platinum atoms available to react with the hydrogen,”
Lefty or Righty? PET Studies Highlight “Mirror Image” Drug Differences
New PET imaging studies at Brookhaven are helping scientists to understand how a drug’s “handedness” affects its performance in the human body, and may lead to the development of more effective pharmaceuticals.
Just like a person, drug molecules can be “lefties” or “righties,” a property determined by the spatial orientation of their atoms. Mirror images of each other, each version of a particular drug molecule contains the identical atoms and identical chemical and physical properties, but can have different effects in the human body. “Our body’s proteins can distinguish the difference between left- and right-handed molecules and react accordingly,” said chemist Yu-Shin Ding. “The results can be quite dramatic.”
Most drugs are mixtures of the lefty and righty versions of the same molecule. In the case of Ritalin, known also as methylphenidate, Ding and her research team found that the right-handed version is responsible for the therapeutic effects of the drug. As a result, if the right-handed version were to be isolated and produced as a pharmaceutical drug, patients may only have to take half of the current dose to get the same effect. This kind of selective production can also help reduce unwanted drug side effects – L-dopa, used to treat Parkinson’s disease, is one example of a left-handed molecule being used because the right-handed version has associated side effects.
Ding and her colleagues are currently studying a host of other drugs to
determine the “handedness” effect, including methadone; GVG, a drug that
has shown promise in the treatment of addiction; and BPA, a drug used for
the treatment of melanoma and brain tumors .
Mapping Human Enzyme Activity
New radiotracers developed by Brookhaven scientists are helping to map an important enzyme’s role in the human body, studies that may facilitate the development of new drugs and lead to a better understanding of brain and body chemistry.
Chemist Joanna Fowler and colleagues have developed radiotracers for mapping the enzyme monoamine oxidase (MAO), a molecular target of drugs used to treat depression and Parkinson’s disease. Using a medical imaging technique called positron emission tomography (PET), Fowler had previously discovered that smokers, who are less prone to Parkinson’s disease, have an average of 40 percent less MAO than nonsmokers. MAO breaks down dopamine, a brain chemical that is important in movement, motivation, and reward.
MAO has an equally important role in the body, where it breaks down potentially dangerous toxins in food. Until now, however, scientists have not been able to image the enzyme’s activity in organs other than the brain. Fowler and her team are now using these Brookhaven-developed radiotracers to look at MAO activity in other organs and determine how MAO levels are affected by smoking and interaction with various drugs. This work may help lead to the development of new drugs to treat or prevent Parkinson’s disease, and help identify other factors that influence MAO levels, including aging and smoking, and their possible implications in health and disease.
“This is important knowledge,” said Fowler, who will receive the ACS’s Glenn T. Seaborg award on Monday for this and other brain chemistry work. “We’re now able to look at the effect of various drugs on the enzyme directly in the body.”