Nanocavities, sized to order 8034scicon.color copy By carefully adjusting the placement of amide bonds between residues in a series of oligomers, chemists have created hollow helices of tunable size. The resulting nanocavities might be useful in catalysis, drug delivery, or ion-carrier applications, according to Bing Gong, associate professor of chemistry at the State University of New York, Buffalo, and coworkers (Proc. Natl. Acad. Sci. USA, published online Aug. 12, The backbone of the oligomers consists of benzene rings linked by amide groups. Three-center hydrogen bonding between the amide hydrogens and alkoxy substituents on the aromatic rings forces the oligomers into curved conformations. For example, a nine-unit oligomer with its amide moieties all placed meta to each other folds into a helix with a cavity about 10 in diameter. Replacing some of the meta linkages with amide groups placed para to one another changes the curvature of the backbone, the researchers report. Thus, a 21-unit oligomer with alternating meta and para connections folds into a helix with a diameter greater than 30 (shown).