The University Record, April 5, 1993

U chemists synthesize gargantaun molecule

By Sally Pobojewski
News and Information Services

U-M chemists have synthesized the world’s largest pure hydrocarbon molecule—a gargantuan sphere with 100 times the volume of a buckyball and big enough to hold 1,000 carbon atoms with room to spare.

Comprised of 1,134 carbon atoms and 1,146 hydrogen atoms, the mammoth molecule has a molecular weight of 14,776. It was created by U-M chemists who are developing synthetic “skeletons” that may someday function like biologically active macromolecules.

The new U-M molecule has a diameter five times greater than the recently discovered geodesic dome-shaped buckyball molecule, which is made up of 60 carbon atoms.

According to Jeffrey S. Moore, assistant professor of chemistry and macromolecular science and engineering, these giant carbon molecules might be combined to function as a light energy harvesting device, similar to a solar cell, that could focus energy from sunlight and transform it into chemical energy. Moore also believes the jumbo molecule, which is essentially a hollow sphere, could have potential applications as a drug delivery system.

Moore and Zhifu Xu, postdoctoral fellow, described the new molecule and how it was produced during a March 30 presentation at the American Chemical Society meeting in Denver.

Synthesized from 94 units of a carbon-based building block called phenylacetylene, the molecule branches off in an unusual repeating, fractal pattern linked by strong triple bonds. “As the molecule grows, its branching arms interlock with each other to form a sphere with many voids and niches inside,” Moore said. “The sphere is stiff. It will bend, but it won’t break or collapse under most conditions.”

The chemical structure of the new molecule has been verified with nuclear magnetic resonance spectroscopy, according to Moore.

Moore and Xu almost gave up on the new hydrocarbon because it was so difficult to get the material to dissolve. Xu spent one full year testing different chemical structures until he discovered that placing molecular fragments called “bulky groups” on the surface of the sphere helped break the bonds that held the individual hydrocarbon molecules together in a solid mass.

“The solubility of this molecule is bizarre to say the least,” Xu said. “We’ve gone from one extreme to the other. Initially, the material was like a rock; it wouldn’t dissolve in anything. Now it’s soluble at room temperature in a variety of common organic solvents.”

Solving the solubility problem was critical to the success of the research effort, Moore explained, because otherwise the molecule would be inert and unable to combine chemically with other molecules.

Unlike many synthetic polymers whose size and molecular weight vary from one molecule to another, the U-M synthetic hydrocarbon sphere varies only slightly no matter how many individual molecules are produced. Its uniformity makes it a valuable chemical “yardstick” scientists could use to measure the size of ultrasmall particles and structures, according to Moore.

A complete description of the new molecule will be published in an upcoming issue of the Journal of the German Chemical Society (Angewandte Chemie). The research was funded by the National Science Foundation.