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Molecular Pony Express

A schematic shows anthraquinone molecules (consisting of three

linked gray benzene rings and pink oxygen atoms) as they

"carry" carbon dioxide molecules across a copper surface.

Researchers have designed a molecule that can carry a couple of carbon dioxide molecules with it as it "walks" in a straight line. It may sound like a stupid molecule trick, but the technique is expected to lead to the new drug-delivery techniques and nanotech assembly lines.

"This is an unprecedented step forward toward the realization of molecular-scale machinery," Ludwig Bartels, a chemistry professor at the University of California at Riverside, said today in a news release. "Our experiments show a means to transport molecules reliably. This will become as important to the molecular machinery of the future as trucks and conveyor belts are for factories of today."

Walking molecules aren't exactly uncommon. In fact, we literally couldn't live without them. For example, hemoglobin transports oxygen from the lungs to your cells, and other types of proteins transport nutrients within those cells. This archived article looks into your cellular machinery, and you'll definitely want to check out this interactive graphic to watch your proteins in action.

In 2005, Bartels and his colleagues made a splash by designing a molecule that could move in a straight line on a flat surface. The latest research, published today on the Science Express Web site, describes a molecule that can pick up, carry and release two carbon dioxide molecules.

"It's significant, because we wouldn't expect atoms to move that way," Talat Rahman, a physics professor from the University of Central Florida and a co-author of the study, explained in a UCF news release. "Atoms tend to move randomly, like dust particles, and getting them to move in a specific direction will help in our understanding and manipulating of the region around atoms."

The molecule that Bartel's group used is anthraquinone, which consists of three fused benzene rings with one oxygen atom on each side (C14H8O2). UC-Riverside says the organic compound is widely used in the pulp industry for turning cellulose from wood into paper.

The researchers set the molecules down on a highly polished copper surface, and used a scanning electron microscope to monitor the molecular Pony Express. 

"Carrying a load slows the molecule down," Bartels said. "Attachment of one CO2 molecule makes the carrier need twice as much energy for a step, and a carrier with two CO2s requires roughly three times the energy. This is not unlike a human being carrying heavy loads in one or both hands."

To get a clearer picture of the molecules in action, check out the videos at Bartels' Web site.

The type of molecule used for Bartels' latest trick represents just one small step toward a nanoscale leap. "Next, we would like to be able to make one go around corners, rotate its cargo or send out photons to tell us where it is," Bartels said.

Eventually, molecular contraptions could be used as multipurpose tools to assemble larger components. They might also be able to carry therapeutic molecules to just the right place to cure an ailing cell - or, for that matter, kill off a cancer cell.

Bartels said creating multipurpose molecules will take some time, but maybe not all that much time.

"Ten years ago, a cell phone could just place calls, nothing else," he observed. "Now it plays MP3 files, organizes your day, lets you send e-mails and browse the Web."

In addition to Bartels and Rahman, the research team included K. L. Wong, G. Pawin, K.-Y. Kwon, X. Lin, T. Jiao, U. Solanki and R. H. J. Fawcett from UC-Riverside, as well as S. Stolbov from UCF.