Tubules self-assemble smaller than DNA.

Just think about building a perfect cylinder with only a few molecules -- a tubule narrower than a helix of DNA.

Not an easy task. Yet Akira Harada and his colleagues, all chemists at Osaka University in Japan, have succeeded. As reported in the Aug. 5 NATURE, the scientists built the tiny tubules from cyclodextrin, a glucose derivative. The tubules measure 15 angstroms in diameter, with an inner core of 5 angstroms. By comparison, an average DNA helix is 20 angstroms across.

To build these tubes, the researchers took advantage of molecular self-assembly. Here, cyclodextrin rings -- which look like lampshades -- line up along a polymer chain (called polyethyleneoxy). "Stopper" molecules then seal off the ends, bonding the rings together. Finally, the center thread drops out, opening up the tubules. "Using self-assembly to make nanometer-sized structures with controlled sizes and shapes," says chemist Angel E. Kaifer of the University of Miami, "is interesting by itself."

Applications for these tubules lie far ahead, but Kaifer does see potential uses: as templates for building other molecules, for example, or as a filter for separating small molecules, or perhaps even as a delivery system. "You could put something inside the tubules, then break them down to release the material," Kaifer explains.