Rudolph Marcus, Nobel Laureate Ė The BNL Connection

from the Brookhaven Bulletin, October 23, 1992.

BNLers, particularly those in the Chemistry Department, cheered last week when the Royal Swedish Academy of Sciences announced that Rudolph Marcus has won the 1992 Nobel Prize in Chemistry for his work on electron-transfer theory, carried out over 30 years ago.

According to Chemistry Chairman Norman Sutin, some of the early definitive tests of Marcus's theoretical work were done here at BNL, and Marcus has continued his association with the Lab through the years. His last visit was in 1987, when he returned for his third and final three-week stay as a Haworth Distinguished Scientist.

Marcus's Nobel Prize-winning work is a mathematical analysis of how the overall energy in a system of interacting molecules changes and induces an electron to jump from one molecule to another. It sheds light on many complex chemical reactions, including photosynthesis, corrosion and electrical conductivity in polymers.

Strong Program Out East

Marcus, a Canadian-born chemist now at the California Institute of Technology, was on the faculty of Polytechnic Institute of Brooklyn from 1951 to 1964. He started working on his electron-transfer theory in the early 1950s and soon discovered that out east, on Long Island, was a strong experimental program at Brookhaven on electron-transfer reactions.

The Lab program had been started by Richard Dodson, now retired, then chairman of the Chemistry Department. Sutin came to Brookhaven in 1956 on a postdoctoral appointment to work with Dodson and joined the Chemistry staff in 1958.

Beginning in 1958, Marcus had a series of formal appointments at BNL, ranging from consultant to visiting senior chemist to research collaborator. Sutin shared an office with him and recalled a great deal of interaction and discussion. "He was quite interested in experimental results, very much in touch with experimentalists and appreciative of their contributions," said Sutin.

He continued, "Theory is not cut- and-dried; it's an evolving thing. We had a lot to do with getting Marcus's theory accepted because our experimental work provided the first verification of several of the predictions of his theory. This, in turn, gave him confidence that it was worth pursuing."
In fact, of Marcus's papers describing electron transfer, seven include Brookhaven Lab under his byline, and four are coauthored with Sutin.

A Fundamental Process

The bulk of chemistry consists of electron transfer in one form or another; it is a fundamental process. To understand many areas of chemistry, biology and physics, one must understand how electron-transfer processes occur, what governs their speed, and why electron transfer occurs in some cases and not in others.

Early BNL studies of electron- transfer reactions used radioactive isotopes to examine the simplest class of reactions, the electron-exchange reaction, In which there is no net chemical change. Such reactions are most conveniently studied by using a radioactive isotope to label the chemical form containing the electron. The chemical forms with and without the electron are then separated as a function of time and their radioactivity determined. This provides a measure of the electron transfer rate.
By the 1950s, - several of the national labs supported by the Atomic Energy Commission, a predecessor to the U.S. Department of Energy (DOE), had developed considerable expertise in working with radioisotopes, a natural outgrowth of nuclear developments in World War II. BNL's Chemistry Department was an ideal location for early experiments on electron transfer because of the expertise here and the availability of radioisotopes from Oak Ridge National Laboratory. The isotopes supplied by Oak Ridge were converted to an appropriate chemical form at Brookhaven.

The results of these studies were surprising: Despite the apparent simplicity of the electron-exchange processes (no chemical bonds were made or broken), the electron-transfer rates varied over a very large range.

Intrigued by Early Results

"Marcus was intrigued by the early exchange results," said Sutin, "and they, in turn, reinforced his interest in electron-transfer theory. He soon extended his early electron-transfer work to include reactions accompanied by a net chemical change, in theoretical work that came to be called the Marcus cross-relation. "

Sutin added, "Our work here led to refinements and extensions of theory. The theory, in turn, suggested new experiments. "The dialogue between Marcus and Sutin continued over the years, reflected by their joint authorship of four papers during 1975-1986.

BNL Acknowledged

Marcus acknowledged BNL in an article on his work in the July 1986 issue of Journal of Physical Chemistry: "Frequent visits to the Chemistry Department of the Brookhaven National Laboratory during this period and discussions there of experiments with Dick Dodson and Norman Sutin served as a considerable stimulus. It was indeed in a conversation with Norman around 1962 that I mentioned the cross-relation to him. Norman had the various rate constants at his fingertips and, to our delight, the relation seemed to work. This result and tests of other predictions were published in 1963. During the sixties and seventies Norman pioneered, among his many other studies, the experimental testing of the cross-relation, its applications to biological molecules (cytochrome c), and the related predictions on the effect of the standard free energy of reaction on the rate."

In the late 1980s, a group at Argonne National Laboratory [see web editorís note] provided the best confirmation of a remaining prediction of the Marcus theory, namely, experimental evidence for the so-called "inverted region" where rates decrease with increasing driving force.

As for Sutin's electron-transfer experiments, they evolved into studies of light-induced, electron-transfer reactions - the reactions that drive photosynthesis. The current program investigates the storage of solar energy through chemical change, and is funded by DOE's Chemical Sciences Division, within the Office of Basic Energy Sciences under the Office of Energy Research.

"It's important to note that our electron-transfer work has always been funded as basic research," said Sutin. "The knowledge gained has significant implications for the design of practical systems involving energy conversion."

- Mona S. Rowe

Web editorís note: That study at Argonne was directed by John R. Miller, who currently leads the group formerly headed by the-now-retired Norman Sutin here at Brookhaven. When Rudolph Marcus received his Nobel prize, both Norman Sutin and John R. Miller attended.

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Last Modified: June 28, 2012