June 23, 2009

Pulled chemical bonds may not break faster

U.S. scientists studying chemical bonds have discovered such bonds do not necessarily break faster when they are stretched.

Our findings contradict the intuitive notion that molecules are like rubber bands in that when we pull on a chemical bond, it should always break faster, said University of Illinois Professor Roman Boulatov, who led the study. When we stretch a sulfur-sulfur bond, for example, how fast it breaks depends on how the nearby atoms move.

Boulatov said the findings also contradict the conventional interpretation of experimental results obtained by other researchers studying the fragmentation rate of certain proteins containing sulfur-sulfur bonds when stretched with a microscopic force probe. In those experiments, as the force increased, the proteins fragmented faster, leading the researchers to conclude that as the sulfur-sulfur bond was stretched, it reacted faster and broke faster.

Our experiments suggest a different conclusion, Boulatov said. We believe the acceleration of the fragmentation was caused by a change in the protein's structure as it was stretched, and had little or nothing to do with increased reactivity of a stretched sulfur-sulfur bond.

The study that included Timothy Kucharski, Qing-Zheng Yang, Yancong Tian, Zhen Huang, Nicholas Rubin and Carlos Concepcion has been accepted for publication in the journal Angewandte Chemie, and is now available on the journal's Web site.