Jim McCusker (left), professor of chemistry, and Dong Guo, post-doctoral research associate
The same principle that causes a figure skater to spin faster and faster as they draw their arms into their bodies has now been used by researchers at Michigan State University to understand how molecules move energy around following the absorption of light.
Conservation of angular momentum is a fundamental property of nature. Astronomers use the principle to detect the presence of satellites around distant planets. In 1927, it was proposed that this principle should apply to chemical reactions, but a clear demonstration of this effect has never been achieved.
Research led by Jim McCusker, professor of chemistry, and published in the recent issue of Science demonstrates for the first time the effect is real and also suggests how scientists might be able to use it control and predict chemical reaction pathways in general.
“The idea has floated around for decades and has been implicitly invoked in a variety of contexts, but no one had ever come up with a chemical system that could explicitly demonstrate whether or not the underlying concept was valid,” says McCusker. “Our result not only validates the idea, but it really allows us to start thinking about chemical reactions from an entirely different perspective.”
The experiment involved the preparation of two closely related molecules that were specifically designed to undergo a chemical reaction known as fluorescence resonance energy transfer, or FRET. Upon absorption of light, the system is predisposed to transfer that energy from one part of the molecule to another. McCusker and his collaborators changed the identity of one of the atoms in the molecule from chromium to cobalt; this altered the properties of the molecule in such a way as to shut down the reaction if the application of the idea of conservation of momentum was correct. The absence of any detectable energy transfer in the cobalt-containing compound confirmed the hypothesis.
“What we have successfully conducted is a ‘proof-of-principle’ experiment,” McCusker noted, “but the formalism that describes the phenomenon should be completely general. One can easily imagine employing these ideas to other chemical processes and we’re actually exploring some of these avenues in my group right now.”
The researchers believe their results could impact a wide variety of fields including molecular electronics, biology, and energy science through the development of new types of chemical reactions.
The paper, Angular Momentum Conservation in Dipolar Energy Transfer, was published in the December 23, 2011 edition of Science. Dong Guo, a post-doctoral research associate, and Troy Knight, a former graduate student and now a research scientist at The Dow Chemical Company, were involved in the research. Funding was provided by the National Science Foundation.
Related Information:
- Science: Angular Momentum Conservation in Dipolar Energy Transfer
- NSF grant helps drive solar energy research
- McCusker Group Homepage
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