Modified Gold Particles Serve As Chiral Adsorbents

Gold nanoparticles decorated with chiral molecules can serve as enantioselective separation media for other types of chiral molecules, according to researchers at Carnegie Mellon University (J. Am. Chem. Soc., DOI: 10.1021/ja908219h). In addition to demonstrating the potential for use in chiral separations, the study may lead to advances in enantiospecific catalysis and sensing applications. Nisha Shukla, Melissa A. Bartel, and Andrew J. Gellman treated suspensions of gold nanoparticles with D-cysteine, L-cysteine, and the racemic mixture. The team then exposed the coated nanoparticles to propylene oxide. Next, they conducted a series of control experiments in which they measured the optical rotation of bare nanoparticles (which are not chiral), cysteine-modified particles, and coated nanoparticles that had been exposed to enantiomerically pure propylene oxide. They observed that L-cysteine-modified gold particles selectively adsorb (R)-propylene oxide and that the D-enantiomer selectively adsorbs (S)-propylene oxide. Exposing a racemic mixture of propylene oxide to one type of modified gold particle results in an enantiomerically enriched solution, they say.