Gargantuan hydrocarbon dwarfs buckyball.

The dream of engineering molecules that can perform biological functions has moved a step closer to reality. Two chemists at the University of Michigan in Ann Arbor have constructed the largest known pure hydrocarbon, which rivals biological macromolecules in size. The new molecule - a lacy, branched polymer known as a dendrimer - has a precisely defined structure and can be produced in surprisingly uniform batches, says Jeffrey S. Moore, who conducted the work with Zhifu Xu. Other large polymers vary in size and weight from one molecule to another, Moore notes.

"Nature has spent a great deal of effort controlling the structure of macromolecules," he says. "If we can do that too, there's a possibility we will be able to do many of the same things that nature has done."

Like the 60-carbon molecule called the buckyball, the new hydrocarbon forms a hollow sphere. But its 1,134-carbon lattice has a volume 100 times larger, with many niches that could be filled. Moore and Xu believe scientists might someday use it to perform tasks such as carrying drugs in the body or serving as a building block for solar cells that trap sunlight for conversion into chemical energy.

To synthesize the new molecule, the team used a carbon-based building block called phenylacetylene. A temperature of 35 [degrees] C to 40 [degrees] C, large amounts of catalyst, and about two days' time brought together the 94 units that must lock into place to form the spherical cage.

Because the dendrimer has a highly repetitive structure and triple-bond linkages, it takes a very stiff form, which made it initially insoluble. Xu and Moore completed the synthesis by attaching "bulky" chemical groups to the molecules to make them soluble. The material can now be dissolved in a variety of organic solvents at room temperature.

The new compound, whose structure has been verified by nuclear magnetic resonance spectroscopy, will be described in detail in an upcoming issue of ANGEWANDTE CHEMIE.