X-Rays Discern Crystal Enantiomers

Conventional X-ray crystallography can identify structures of enantiomers, but it can't distinguish between right- and left-handed crystals. Now, a group led by Yoshikazu Tanaka of the Japanese research institute RIKEN has used circularly polarized synchrotron X-ray beams to elucidate the handedness of crystals (Phys. Rev. Lett. 2008, 100, 145502). Other techniques to identify crystal chirality typically require either having the crystal interact with another chiral material or slicing or mounting a crystal to view it in a microscope. The researchers used the polarized X-ray technique, called resonant Bragg diffraction, to study two enantiomers of quartz and found that the two crystal types reflect different X-ray intensities depending on right- or left-circular polarization. The approach could be a useful screening tool for applications that require a chiral environment such as biomolecular interactions or selective reflection by liquid crystals in optical applications. "While this synchrotron-based technique may not have many immediate practical applications, Tanaka and coworkers have demonstrated a new and supremely elegant process for characterizing chiral materials," says research scientist Robert M. Hazen of Carnegie Institution for Science, Washington, D.C.