The Driving Force of Uncertainty: A Conversation with Chemist Rudy Marcus
By Katie Neith
On July 22, 2024, Caltech announced a new research center established in honor of theoretical chemist and Nobel Laureate Rudy Marcus. It was a big week for Marcus: Just a day earlier, he had celebrated his 101st birthday.
For nearly half of his life, Marcus has been on the Caltech faculty. He joined the Institute in 1978 as the Arthur A. Noyes Professor of Chemistry and still maintains an active small group that explores questions in theoretical chemistry. In 1992, Marcus received the Nobel Prize in Chemistry “for his contributions to the theory of electron transfer reactions in chemical systems,” which are fundamental reactions that underlie a plethora of chemical and biological processes.
Caltech magazine recently talked with Marcus about his prolific career and what keeps him curious in this second century of his life.
Two former postdoctoral scholars, Jack Zhang, who studied under you, and his wife, Mary Luo, pledged $30 million this summer to endow the Rudolph A. Marcus Center for Theoretical Chemistry at Caltech. How did you feel when you found out?
It was a surprise! They didn’t tell me they were doing it, but I’m delighted anytime somebody gives a generous gift to Caltech. They’re a wonderful couple, two very smart and very nice people. They’re an ingenious pair, and they’ve done fantastically well, which makes me happy.
Jack said that when they first got started in environmental chemistry, before their pharmaceutical work, I wrote a letter to the Navy about the project, and they got their first grant. I think they’ve never forgotten that.
Their gift will support fellowships, instrumentation, and faculty recruitment. How do you hope the center will work to advance chemistry?
Any time you have a substantial amount of money to bring in students and perhaps to attract some faculty, it’s a good thing. The conditions under which you're doing your research are important, so it’ll certainly help there. For new people coming along, I hope it will attract the same high-quality students and faculty that are already at Caltech; such gifts can help Caltech to achieve that goal.
You clearly left an impression as a mentor to Zhang and Luo, and you have guided many other students and postdocs over the years. But how have the younger generations impacted you?
I’ve always enjoyed interacting with people. What’s important about students is the freshness and the intensity with which they approach a problem. Having a number of students to talk with, and, in some cases, to bounce ideas off or even get ideas from, is something I really enjoy. Ideas spring up when you’re in contact with new experimental results, especially if you can keep an open mind and not just be focused on one thing, and students have helped me over the years to keep that in mind.
When you were in school, you studied experimental chemistry but soon moved to a more theoretical approach. Why?
When I was growing up in Canada, there were no theoreticians in chemistry. None. And so, I did experiments. After getting a PhD at McGill University, and after a little over two years of postdoctoral studies at the National Research Council Canada, I realized that I was not very happy. Although I enjoyed building apparatus in the lab, I also realized that I no longer really enjoyed doing experiments. So, a friend and I—we got our PhDs at the same time from McGill—started a two-man seminar. Each week, one would read or describe some theoretical paper to the other one, and we tried to learn theory that way. We even took one of the theories, a popular one, and tried to apply to our experimental results some computations following the equations that were in that theory. And that was far more of interest to me than what I was doing.
So, I applied to do research on theory with six people in the US. One of them—Oscar Rice at the University of North Carolina at Chapel Hill—said that he would apply for a Navy contract, and if he got it, I could come down as a postdoc. He was a very well-known scientist. He won the [American Chemical Society] Pure Chemistry Award the second year it was given. The first year, Linus Pauling won. So that was an indication of the kind of scholar that Oscar Rice was.
“What’s important about students is the freshness and the intensity with which they approach a problem. Having a number of students to talk with, and, in some cases, to bounce ideas off or even get ideas from, is something I really enjoy.”
Oscar got the contract, I went down, and immediately it was like a breath of fresh air. I was reading and reading and reading all this theoretical work. His idea of trying to train me was that once a week we would meet, and I would pick some theoretical paper in the literature and try to describe it to him.
That was just a wonderful, wonderful time, and Oscar was really the ideal person for me, as it turned out, for making a switch from experiment to theory. I think the effect of that laboratory experience, plus the undergraduate and graduate training, was that I tended to think more as an experimentalist, even though I was very strongly influenced by the nature of theory. And that’s still the case.
After North Carolina, you went on to teach at the Polytechnic Institute of Brooklyn (now called the New York University Tandon School of Engineering) and the University of Illinois before coming to Caltech in 1978. It was early in your career in New York that you started working on a theory to explain the rates of electron transfer reactions that now bears your name. What is the origin story of the Marcus theory?
I started working on the electron transfer theory in Brooklyn and finished it there. Where it began was in a tiny corner of chemistry. Scientists were studying what’s called isotopic exchange reactions of the electron transfer type and were exploring why some reactions were slow and some were fast. It turns out these reactions were the simplest of reactions in all of chemistry. Just an electron is transferred from one reactant to another—no bonds broken. That simplicity permitted me to isolate in one’s own mind the important factors that affect how fast the reaction is or how slow it is.
After hearing about the problem, the process of thinking of the idea and of how to handle it, and writing the first paper took just one month. I’ve never done anything so quickly again. I’ve spent as much as a year on some problem, but this time it was one month from hearing about it to having an equation. It turns out that if you’re doing the theory on your own, and you have a lot of energy, you can put a lot into it in a short piece of time.
You’ve been at Caltech for more than 45 years. What first drew you here, and what has kept you?
Caltech is one of the top places for science. It has exciting scientists, like Harry Gray, who was one of the people who brought me here, and the late Ahmed Zewail, who also helped recruit me. Certainly, the quality of people is so strong. The atmosphere and the interaction of faculty and students is very special, and I’ve enjoyed that interaction from the moment I first arrived here.
You won the Nobel Prize in 1992 for your work on the theory of electron transfer reactions. How did that change your life?
Of course, when one’s work gets recognized in a such a concrete way, it feels good. But the most important aspect is the work itself. That recognition has certainly opened up doors, but I’ve also been lucky that I’ve always had the freedom to do my work. Long before the Nobel Prize, I had time to think about problems; I still enjoy thinking about problems and how to try to solve them.
What are you most proud of in your career so far?
On the one hand, there’s the research. On the other hand, there’s the social aspect. And I think that I provided a supportive environment for students. I’ve never had a large group, but I’ve always enjoyed interacting with students. And I know my research advisor at McGill University, Carl Winkler, liked having a group of students around, so he was an example of that.
Another experience is hearing about some problem or experiment that maybe hasn’t been explained well, or perhaps has been explained in the wrong way. Then one thinks about it and brings in this idea and that idea that one heard from various sources, and, suddenly, you’re building a theory. What strikes me in some of the works is the unexpected nature of how I may start writing a paper, and I’ll end up on a different course. Of course, there are always some disappointments. Not everything works out. Sometimes one may spend too much time on some problem that didn’t amount to much. So, there are experiences like that, but there’s enough of the other that I found exciting and still find exciting, so I keep on going.
What are you currently working on in your research group?
There are several topics. One, which we have a series of papers in progress, is understanding the mechanism of biological motors. Inside all of us, there are many kinds of biological motors. Some pump ions across the membranes. Some are associated with muscles. Some are associated with ribosomes—all sorts of systems. Some of these biological motors have been studied at the single molecule level—that’s how high the spatial resolution is now. There are several experiments in that field, and we looked at one question: How do they convert chemical energy to mechanical energy and vice versa?
And in a totally different field, there’s our work on electron transfer. Researchers have been able to study faster and faster reactions with better and better experimental techniques; they can now look at reactions that take 10 femtoseconds, for instance. Well, that’s 1015 times faster than most chemical reactions, so that’s very fast. New phenomena show up. One project that we’re working on is to bring different kinds of experiments together and try to explain, in simple physical terms, some of the experimental results.
One must be prepared to go into territory where one doesn’t know if it’s going to be successful. You have to be willing to flounder around, and I’ve done a lot of floundering over the years.
You recently celebrated your 101st birthday. What motivates you to keep working?
It’s hard to believe! I still get excited by problems that I hear about. I’ll think, Here’s this result, how can I develop some equations to interpret that? It’s hearing about certain results—that’s the stimulating factor. You hear about some results—typically experimental, but on two occasions for me from computational results—that must have an explanation. So, you work on it, you try various approaches, and you do a fair amount of reading, because there’s no point in reinventing the wheel. Part of the excitement is not knowing where the approach is going to really go. In some cases, the answer turns out to be very simple, or somebody turns out to have done something like it, and there’s a bit of a letdown. But there’s often that uncertainty of where the research is going, and it’s a driving force for me.