A chemist who's more than a chemist

Chemistry Professor David Leitner's well-rounded career now includes being named a prestigious American Physical Society fellow

4/8/2013 - By: John Trent
Leitner

Years ago, when David Leitner made a somewhat last-minute, senior-year decision and "somehow ended up getting another degree in chemistry" while an undergraduate at Cornell University in Ithaca, N.Y., a definite course had been set.

Leitner didn't realize it at the time as he graduated from Cornell with not one, but two, undergraduate degrees in chemical engineering and chemistry, but both degrees have come in handy. More than anything, they've ensured that Leitner's career as a university professor has been special.

"I enjoy my job immensely," Leitner said recently during an interview in his office on the third floor of the Chemistry Building. His research and teaching, though it appears to be quite specific in nature, has also been, in many ways, collaborative and cross-disciplinary.

The American Physical Society has taken notice of the consistent excellence of Leitner's work, as he received news in November 2012 that he had been named a fellow in one of the world's most prestigious scientific societies.

"I'd been involved with the society's Division of Chemical Physics for a number of years," said Leitner, whose term as secretary/treasurer of the division ends this year. "Still, it was certainly a great surprise to get the news. It's a great honor, and I was humbled to receive it, especially knowing some of the people in the class of 2012."

Leitner, a professor of chemistry at the University since 2000, has had a strong influence on his students in theoretical and biophysical chemistry, which are also the general fields of research he has focused on since arriving at the University.

Yao Xu, a 29-year-old Ph.D. student in the University's Chemical Physics program, said Leitner's reassuring personality and firm knowledge in the field have been the driving forces behind Xu's five-year experience in the program.

"Dr. Leitner is definitely a great mentor with a passion for science, compassion for students, and commitment to excellence," Xu said. "He has been helping me a lot during my studies here. Dr. Leitner was the person who inspired my interest in fundamental problems in chemical physics and guided me to independent research. He always encourages his students to pursue their own research direction and to interact with researchers from different fields."

Xu said he is constantly amazed at Leitner's deep involvement with all aspects of science. Xu said Leitner has served as a judge for the Western Nevada Regional Science Fair in Reno, and has served as a coach for the 2013 Davidson Academy Science Olympiad team.

Xu said that unlike other mentors, Leitner does not give the young man "a direct hand to solve a problem."

"But," Xu said, "Dr. Leitner provides me an ample amount of time so that I can concentrate on work and focus on a solution until the problem is solved. Every time when I successfully solve a puzzle, I learn that it is really more than just gaining knowledge and problem-solving skills that Dr. Leitner is teaching me; he's helping me achieve independence in my research and throughout my life."

As Xu said, Leitner isn't afraid to come at his chemistry with a decidedly cross-disciplinary bent. Perhaps it has something to do with those two undergraduate degrees. Or, perhaps more to the point, it simply helps Leitner better conceptualize his teaching and research.

In addition to the Chemical Physics program that he directs, Leitner regularly teaches graduate-level courses in statistical mechanics and quantum mechanics, as well as courses in spectroscopy and advanced topics in statistical mechanics.

"I enjoy teaching students in this wide range of disciplines," Leitner said. "It's been a challenge, but it's been very interesting, very helpful to me."

A great example of Leitner's versatility as a teacher of chemistry can be found in a physical chemistry for biochemistry and biology majors course that Leitner began teaching in fall 2001. The course started with "25 or so students at the time," he said. "Now, there were a little over 80 that I taught this past fall. To teach at the undergraduate level, to students who are probably more interested in their fields of biochemistry than physical chemistry, has been a something I've really enjoyed."

He said such a well-rounded approach reminded him of his graduate studies at the University of Chicago.

"The boundaries were quite open," he said. "My first year there my advisor was on sabbatical at Oxford, so I was able to interact with a very different group of post-docs in condensed matter physics. We ended up publishing a paper together. It was fun, and I came to realize that I enjoyed working with different groups. Doing the lecture courses today, in a lot of different areas, has helped me occasionally branch off into those areas."

So much so that Leitner found an unlikely research partner in 2003 in Matt Enright. As a junior at Mammoth (Calif.) High School, Enright, who was interested in computers and computer simulation, contacted Leitner and was welcomed into the chemistry professor's lab.

The two moved from studying physical properties of individual protein molecules - proteins being one of the prime thrusts of Leitner's research - to carrying out a statistical analysis of about 200 molecules to explore common physical properties. Enright wrote original analysis software, produced charts and data, and together, the two published a paper on the results. Another paper was subsequently published on energy transfer in a large number of simulated proteins in water.

"Dr. Leitner provided the perfect amount of structure for me to learn and adapt," said Enright, who went on to graduate from Cal Poly with a degree in computer science and today works for a small video game startup in southern California. "He could explain molecular physics in a way that conveyed both the basic concepts and the motivation for the research. He also welcomed tangential study, encouraging me to incorporate software optimization and computer graphics where they could complement the primary work."

Enright said he had no idea of Leitner's accomplishments, which probably is not all that surprising, given Leitner's soft-spoken and modest nature.

"He spoke very little about his other research, so I developed an appreciation for him as a teacher first," Enright said. "Only when I began to understand something of the field did his achievements come to light, and today I am grateful to have contributed in some small way to his work. Dr. Leitner gave me a wonderful opportunity in three summers to be involved in the creation of two published papers."

Enright said he will always remember and value the encouragement he received from Leitner.

"The trait that stands out most for me is Dr. Leitner's ability to incubate motivation," Enright said. "At no point was any of my early work criticized, and my original ideas and contributions were incorporated and encouraged. This atmosphere led me to expand my understanding and accomplish more than my high school education had prepared me for. In particular, the appreciation he expressed for my cross disciplinary application of computer science remains some of the fondest memories of my growth as a programmer."

Of the work that a veteran chemist was able to create in concert with a teen-aged research collaborator, Leitner smiled and said, "We published what is still one of my favorite papers together. Matt was a very bright young person, he was really remarkable."

And, Leitner added, it was his young research partner's skills that allowed the two go into great computational depth in protein data banks. This was an essential part in figuring out key calculations of some of the geometric properties involved with the research.

"We kind of started a trend six or seven years ago," Leitner said, as other studies are now using similar methods.

The stories about his current and past students, as well as the enjoyment Leitner feels for his wide range of teaching he does, tell only part of Leitner's career story. His research agenda is full of important questions that have great implications not only for chemistry, but for wide-ranging applications of the knowledge that is established.

Much of Leitner's focus in recent years has been on developing maps of communication processes within proteins. When, say, a small molecule binds to a protein, that information can be transferred to the other binding sites in the molecule, which in turn affects the rate at which other small molecules bind. This happens when oxygen binds to hemoglobin, the protein that carries oxygen into the blood stream.

"We've been developing for the last few years ways to map these communication paths," Leitner said. "In a general sense, we're really just interested in how a folded polymer can transfer that kind of energy. What's really interesting and gratifying is that much of what we've learned in our studies of proteins could be extended to other fields."

Leitner said one of these areas has been interest in "thermal transport on the nano scale. There are engineers who are very interested in designing small circuits where heat build-up can become quite severe. They want to design materials that can drive heat away efficiently."

To that end, Leitner has helped organize meetings bringing together physical scientists and engineers, "to find out more about thermal transport, how it sometimes occurs so efficiently in molecules, and to try and see what we can learn to design other materials with properties like that."

Leitner's other major research focus concerns theories of vibrational dynamics in molecules. To understand his work, one must take an imaginary fantastic journey into the eye, where a protein called rhodopsin is located, and then travel even further, "where the action is, at least initially, which is a much smaller piece of that protein, retinal, which absorbs light."

The first step in vision involves the structural change of retinal following the absorption of light.

"It happens very quickly and efficiently," Leitner said. "Retinal, the chromophore in rhodopsin, a protein in the eye, absorbs light and changes structure in less than a trillionth of a second. It's extraordinary. The process occurs so efficiently because the vibrational dynamics of the chromophore and protein facilitate the reaction.

"What we've been very interested in is trying to understand how vibrational energy dynamics influences rates of chemical reactions, at times facilitating fast and efficient reactions. That's what happens in protein photosensors like rhodopsin."

And if this isn't enough, Leitner is also involved with the understanding of properties of water near the surface of a protein.

"How do properties of water change near the interface with a protein?" he said. "We carry out computer simulations to explore that question. We've recently been looking at anti-freeze proteins in certain kinds of cold-water fish, which helps cells function despite the extremely cold surroundings. WE have been collaborating with an experimental team to learn about the interactions between these proteins and water."

Taken together, David Leitner's career to this point has been remarkably dynamic, incorporating the talents and knowledge found in other disciplines in an effort to find the best scientific insights he can produce.

"There are areas I'm involved with now that, 20 years ago, I could not have seen myself getting involved as a graduate student," he said. Then he added, with a laugh, "At that time, I don't know if I was that interested in biology. What I've found, though, is that science and chemistry and what I'm doing now, it's not just the static structures we see in textbooks. It's the dynamics, all of these different and exciting and efficient movements and reactions, where we learn a lot about how things work.

"And when we do this, and think this way, we can learn so much more."

Then Leitner thought back to the fateful day that he decided to add that second major at Cornell. It was a lot of extra work, but it has meant a lot of extra satisfaction for one of the campus' finest teachers and researchers.

"So in a way," he said, "since starting out as an engineering student, I think I've come full circle."


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