Magnetic Field Skews Molecular Handedness

Magnetic fields might have a hand in the "handedness" of molecules, two physicists say. Using a powerful magnet, they have shown that magnetic fields can influence the selective destruction of left-handed or right-handed molecules. The researchers argue that this might help explain why almost all creatures live on left-handed amino acids and right-handed sugars.

In 1848, Louis Pasteur discovered that sodium ammonium tartrate crystals came in two varieties that are mirror images, just as your right hand is a mirror image of your left. These two varieties rotate light in different ways. Inspired by Michael Faraday's demonstration that magnets rotate light, scientists from Pasteur onward have tried--and failed--to use magnetic fields to influence whether right-handed or left-handed molecules are produced in a chemical reaction, a process called enantioselection. In the 1980s, however, scientists realized that mirror-image molecules, when placed in a magnetic field, absorb light at slightly different rates, a property called magnetic dichroism.

Now a team of physicists from the Grenoble High Magnetic Field Laboratory in France has finally demonstrated that magnetic dichroism can shift the proportions of left-handed and right-handed molecules in a solution. The team used an unstable chromium complex that breaks down even faster if it absorbs a particle of light. The team put a small dollop of the molecules in a powerful magnetic field and shined a laser through. One of the molecules absorbed light more readily than its mirror image and was more likely to break down, Geert Rikken and E. Raupach report in the 21 June issue of Nature. The solution quickly became enriched in the less absorbing molecule.

Experts say this is one for the record books. "It's the first time, ever, since Pasteur tried it over 150 years ago, that anyone has genuinely observed a magnetic field induce absolute enantioselection," says Laurence Barron, a physical chemist at the University of Glasgow. The buildup of certain-handed molecules under the lab's strong magnetic field wouldn't be as pronounced in Earth's magnetic field, but Rikken says that even a minuscule excess of one mirror image over another--such as left-handed amino acids over right-handed ones--might help explain why life prefers one handedness over another.