System Detects ’Evil Twins’

Hank Hogan

In the pharmaceutical industry, many enantiomers, or mirror-image molecules, are harmless fillers, but some are truly evil twins that can cause birth defects or other health problems. Accordingly, the US Food and Drug Administration requires pharmaceutical companies to quantify the enantiomers that they produce in the manufacturing process. An optical system currently in development should make that task much easier.

The trouble with the molecular twins is that they are chemically identical. "The relationship is the same relationship that our right and left hands have to each other," explained Donald R. Bobbitt, associate dean for research and a professor of chemistry and biochemistry at the University of Arkansas.

Bobbitt's team, therefore, focused on another distinguishing characteristic of enantiomers: The right- and left-handed molecules polarize light in opposite directions. This has been used to determine the enantiomeric ratio in small samples.

The new system combines, in real time, the output of a polarimeter and an ultraviolet detector, which provides information both on the degree of polarization and the mass of the sample. Combining and normalizing the detectors' signals yields the enantiomeric ratio, which could be used as a quality-control check of a finished product or for process control during manufacturing.

Drug purity

The potential, then, is for purer, safer drugs. The system also may lower the costs of manufacturing, since it could be less expensive to segregate a desired product from the mix than to develop a chemical reaction that produces it.

Several companies collaborated with the researchers on the project, including PDR-Chiral Inc. of Palm Beach, Fla. A commercial version might combine the detector and polarimeter into a single instrument.