Molecular template makes nanoscale helix

Using ribbons made of organic molecules as minuscule templates, researchers have coaxed a semiconductor material into tiny helical coils. Made of cadmium sulfide, the helical structures could serve as components of future nanoscale sensors and other devices, says Samuel Stupp of Northwestern University in Evanston, Ill.

NANOSCALE TEMPLATE Cadmium sulfide (yellow) grows on a twisted ribbon template (blue). M. Banas

Stupp and his Northwestern coworkers Eli Sone and Eugene Zubarev made the templates for the cadmium sulfide helices from molecules dubbed dendron rodcoils. When added to solvents such as ethyl methacrylate, dendron rodcoils assemble into twisted ribbons that are 2 nanometers thick.

After making these, the researchers added cadmium nitrate to the mix and then pumped in hydrogen sulfide gas. Cadmium sulfide precipitated on one face of each ribbon, forming a single, spiraling helix. The structures, which resemble telephone-receiver cords, had diameters of about 25 to 30 nm, and the spacing of their twists was about twice that of the ribbons’.

The researchers suggest that the spiral structures might have unusual electronic, photonic, or catalytic properties. Since the helices can form as either clockwise or counterclockwise spirals, they might prove useful in detecting or making mirror-image varieties of so-called chiral molecules, says Stupp. “So, there’s this interesting twist,” he muses.

Stupp, Sone, and Zubarev report the work in a May Angewandte Chemie International Edition.

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