Synthesis of right- and left-handed silver nanohelices with a racemic gelator

As a new racemic gelator, 2-acryloylamide-dodecane-1-sulfonic acid (ADSA) was observed to form an organogel with chloroform and tetrahydrofuran. Transmission electron microscopy (TEM) observation for the stained gel from chloroform revealed helical ribbons. Templated by these, both right- and left-handed silver nanohelices were synthesized by reducing the adsorbed silver cations onto the ribbons with sodium borohydride. Interestingly, both opposite-handed helices at the same nanohelice and double-stranded silver nanohelices were observed. A possible model for the auto-optical resolution of the racemate into helical ribbons and the template synthesis of silver nanohelices was suggested on the basis of a stereochemical consideration along with the hydrogen bonds and hydrophobic interaction of long alkyl chains. The mechanism was supported by X-ray diffraction and FT-IR spectra and high-resolution TEM observations.