Cross Sections: The UT Physics Newsletter/Research Highlight: Dr. Bob Compton Tackles Pollutants Threatening the Smokies (Fall/Winter 2002)

Dr. Robert Compton is working to help save the Great Smoky Mountains one molecule at a time.

Dr. Compton, a professor in the physics department and the Paul and Wilma Ziegler Professor of Chemistry, uses infrared spectroscopy to track molecules from the sun to the earth in hopes of finding out if there are any as-of-yet undiscovered pollutants lurking in the Smoky Mountain area.

His group began recording spectra this fall, although Dr. Compton’s interest in infrared spectroscopy goes back to his days as a graduate student and the influence of a physics department legend.

“In a way I got started with inspiration from Alvin Nielsen. I took an infrared spectroscopy course from Alvin in 1963,” he said. Another course with Dr. Bill Fletcher in chemistry intrigued him further. The current project is an offshoot of the physics department’s complex systems laboratory group.

“It really started with looking over the shoulder of (Physics Professor) Bill Blass and his Ph.D. graduate student (now a post-doc) Stewart Hager,” Dr. Compton said. “When I saw that they were looking at the infrared spectroscopy of atmospheric nitrous oxide, it occurred to me that we should be doing that with regards to understanding what’s going on in the Knoxville-Smoky Mountain area. Knoxville has recently been designated as one of the most polluted cities in the country.”

The questions for him, he said, became, “What’s going on in terms of atmospheric air pollution in East Tennessee? And how does that affect the health (trees, etc.) of the Smokies?”

A number of years ago Dr. Compton brought a high resolution infrared spectrometer to UT from the Oak Ridge Gaseous Diffusion Plant as part of a $390,000 ERLE (Energy-Related Laboratory Equipment) grant. This machine was used as a trade-in for a newer state-of-the art spectrometer purchased through funding from the physics and chemistry departments, the Center for Environmental Biotechnology, and the College of Arts and Sciences.

“That allowed us to put a really good spectrometer on the sixth floor of SERF,” Dr. Compton said.

Another key piece of the equipment was already in place, thanks to Stewart Hager.

“Stewart had developed an important component in all this,” Dr. Compton explained. “He had worked at Boulder one summer studying atmospheric air pollution using these types of technologies and he knew how to make what’s called a suntracker,” a set of mirrors that accurately tracks the sun and reflects sunlight down from the roof into the FTIR (fourier transform infrared spectrometer) on the sixth floor of SERF.

Dr. Blass had made sure that a “hole” was incorporated in the new SERF building extending from the roof to the sixth floor. The FTIR is a powerful tool for measuring atmospheric trace gases by producing an infrared absorption spectrum that is like a molecular “fingerprint.”

“What happens,” Dr. Compton said, “is that we have the sunlight coming down through the atmosphere (stratosphere and the troposphere) producing an absorption spectrum. From that we can tell what gases exist between the sun and the earth.

“The spectrum changes dramatically as a function of the angle that the sun makes with the zenith,” he continued.

Absorption is highest when the sun is at the horizon (e.g., sunrise and sunset) and lowest when it’s at the zenith.

“You can follow both of those and you can compare the gases in the atmosphere as the sun comes in through the morning and as it goes through the evening,” Dr. Compton said. “Hopefully we’ll be able to see what differences there are in the atmosphere of the Smoky Mountains. There are gases that we know are there that we can quantify, like ozone and nitrous oxide,” Dr. Compton went on to explain. “Ozone is one of the key molecules that we want to track. Ozone is important because if you want to know the ozone concentration, you can’t go out and take a gas sample and bring it back to the lab. Ozone is so reactive; you put it in a cylinder and it’s gone.”

Infrared spectroscopy offers a solution because the long pathway from the sun to the earth offers a broader spectrum for tracking and offers a method for real-time analysis of atmospheric gases.

“My own personal interest is whether there are molecules in the atmosphere that have not been detected yet,” he said. “What possible influences are there that nobody has really considered?”

While the concept of using IR spectroscopy to track atmospheric pollutants is not unique, the regional angle is what differentiates UT’s work.

“I think we’re probably the only ones studying the Smoky Mountains using sunlight as the IR source,” Dr. Compton said. “Every environment has a different set of gases, a different set of chemistry,” he said. “We definitely have a way to quantify, in real time, some of these gases, and hopefully we’ll identify some that haven’t been thought about—some of the complex atmospheric chemistry that may be unique to the Smoky Mountains.”

Once the group, which also includes chemistry graduate student Jeffrey Steill, records a significant amount of data, the next step will be to write proposals for outside funding.

Chirality and Negative Ions

Meanwhile, some other research endeavors capturing Dr. Compton’s time and attention are the chirality of biomolecules and negative ions.

The chirality studies, sponsored by the National Science Foundation, have to do with understanding the molecules of life. Dr. Compton explained that amino acids can exist as either of two different mirror image conformations. Chemists refer to these as L- or D-amino acids. This is also sometimes referred to as the “handedness” of the molecule. Mysteriously, all proteins present in life supporting molecues are L-amino acids.

“The big mystery is why,” he said. “At the present time we don’t know the answer and we may never know the answer to this question. But we’re trying to do experiments that may shed light on the puzzle.”

Chirality in this context is important because it can have serious consequences on public health.

“You really want drugs with a ‘handedness’ that’s useful to the body,” Dr. Compton said. “Some drugs are known to be beneficial if they are of one handedness and poisonous or dangerous on they are of the mirror image handedness.”

One notorious example is Thalidomide. On one hand, it may alleviate morning sickness in pregnant women. On the other, it is known to cause birth defects.

Dr. Compton said that only about 70 of the 350 drugs presently used are enantiomerically pure (enantiomers are molecules that are non-superimposable mirror images of each other). The Food and Drug Administration is moving toward requiring all drugs to be enantiomerically pure. Pulsed lasers might offer a way to help make these enantiomerically pure molecules. This work is a team effort with Dr. Dick Pagni, an organic chemist.

Another research area for Dr. Compton is the study of negative ions.

“That’s what I’m noted for, if anything,” he said. “After doing research on negative ions with Dr. Tom Bailey at the University of Florida in 1962, I came to work with Sam (Hurst) on negative ions and I’ve been doing it ever since. More recently my work has been with dipole-bound negative anions.”

Working with graduate student Nathan Hammer, he has created about 40 dipole-bound anions, and while some have been previously studied, most are being observed for the first time. These anions are made by transferring an electron from an excited atom to the positive end of a polar molecule of interest. The donor atoms used are atoms that have just one electron in their outermost electron shell – the alkali metals. The excited atom is made by laser excitation. A main goal of this research is to attain accurate electron affinities for each of these molecules to better understand the electron transfer reaction.

Probably the most important contribution in this area is the study of multiply charged negative ions. Not happy to add just one electron to a molecule, Dr. Compton and colleague Dr. Al Tuinman of the chemistry department have been able to add two, three and four extra electrons to many molecules. This is a field started by this group a number of years ago and has broad implications to many areas of pure and applied research. John Fenn won the 2002 Nobel Prize in Chemistry for his research in electro-spray mass spectroscopy, a technique that relies upon the formation of multiply-charged anions in the gas phase.

Dr. Compton has discovered what he calls the “coulomb barrier” for the removal (or addition) of an extra electron to a negative ion. This coulomb barrier prevents the escape of the extra electron much like the coulomb barrier which acts to delay the decay of the nucleus to produce an alpha particle.

Also, Dr. Compton and his colleague (Dr. Robert Hettich at ORNL) have demonstrated that many doubly charged negative ions are more stable toward electron loss than the parent singly charged anion as a result of the coulomb barrier.

Dr. Compton’s chemical physics research won him a College of Arts and Sciences Senior Faculty Research Honor in October. More information about his work is available on his Web site at: http://web.utk.edu/~rcompton/.

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