"Proteins -- the molecular machinery of living cells -- work because they fold into very specific three-dimensional structures," said Jeffrey Moore, a professor of chemistry and a researcher at the university's Beckman Institute for Advanced Science and Technology. "By applying the principles of polymer physics, we designed an all-carbon backbone that spontaneously folds into a compact helical structure."
As with proteins, the folding process of the synthesized molecule is reversible, Moore said. Unlike proteins, however, the molecule has no hydrogen bonds to help drive the transition.
"The polymer backbone consists of a string of up to 20 benzene rings held together with covalent bonds," Moore said. "The molecule is guided through its folding transition by nondirectional interactions and local constraints due to the covalent structure of the backbone. Weak, attractive forces between the rings cause them to rotate and stack one upon another."
The resulting helical structure has a tubular cavity that could be used to bind a variety of metals, small molecules and reactive species, said Peter Wolynes, who holds the James R. Eiszner Chair in chemistry. "The cavity could hold things in specific orientations to perform selective chemistry -- for example, to catalyze reactions. In fact, the folding of linear polymers may provide a synthetically simple means of generating new three-dimensional molecules that could potentially equal the biopolymers in their complexity and functionality."
Future applications aside, the current experiment also sheds some light on the roles that hydrogen bonds play in the folding process, Wolynes said. "There has been considerable debate over the importance of hydrogen bonds in determining the shapes of protein molecules. Some researchers believe the main structure is caused by hydrogen bonds, while other researchers believe the folding process is governed by other, less-defined molecular forces."
By eliminating the hydrogen-bond factor from their polymer backbone, the U. of I. chemists showed that nonspecific forces alone can guide intramolecular self-organization. "Since our polymer formed helices in the absence of hydrogen bonds, it is clear that hydrogen bonds -- while they still may play a part in the folding process -- are not an absolute requirement for this behavior," Wolynes said.
The scientists report their findings in the Sept. 19 issue of Science. Graduate research assistant James Nelson and visiting postdoctoral research assistant Jeffery Saven were key participants in the research.
Journal
Science