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Education

A Chiral Anniversary And Other Discoveries In Wine Science

by Sarah Everts
October 7, 2013 | APPEARED IN VOLUME 91, ISSUE 40

 

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Credit: Wikimedia Commons
Pasteur: Discovered molecular chirality as a young whippersnapper.
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Credit: Wikimedia Commons
Pasteur: Discovered molecular chirality as a young whippersnapper.

You realize a guy is destined for greatness when he discovers molecular chirality at age 25. So it was for Louis Pasteur, who, as a budding young scientist and newly minted Ph.D., decided to take a closer look at the tartaric acid crystals often found in old wine barrels. In doing so, he made a groundbreaking discovery about molecular symmetry.

On Oct. 11, folks at Ecole Normale Supérieure (ENS), in Paris, where Pasteur realized chirality, will celebrate the event’s 165th anniversary. Students will don period costume from the mid-1800s to deliver a speech ­Pasteur gave about the research, says Ludovic Jullien, director of the ­chemistry department at ENS. The reenactment is part of a ceremony to install a commemorative plaque at the institution, given by the American Chemical Society’s Division of History, to honor Pasteur’s discovery.

“Normally in these sorts of ceremonies, you invite a lot of famous scientists to give talks,” Jullien says. But because this prize is about work Pasteur did shortly after earning his doctorate, “we thought it would be better to include graduate students in the ceremony,” Jullien adds. “The idea is to inspire them—to show them what’s possible.”

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Credit: ENS (Ecole Normale Supérieure)
Old School: Pasteur would have worked in a lab like this one at ENS when he discovered molecular chirality.
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Credit: ENS (Ecole Normale Supérieure)
Old School: Pasteur would have worked in a lab like this one at ENS when he discovered molecular chirality.

When Pasteur set out to study tartaric acid, his contemporaries had already shown that if crystals from wine barrels were dissolved in solution, they could rotate polarized light. We now know that’s because grapes contain a single enantiomer of tartaric acid, the (+) version. During Pasteur’s era, some researchers had reported that when a factory manufactured tartaric acid, part of the crystalline product wasn’t able to rotate polarized light, a conundrum Pasteur wanted to resolve.

The young scientist first painstakingly analyzed the mysterious side product under a microscope, separating two different types of crystals he saw there. Then he showed that, when dissolved, one set of these crystals rotated polarized light in exactly the same way the “natural” (+)-tartaric acid did whereas the other set of dissolved crystals rotated the light in exactly the opposite direction.

In a series of papers published beginning in 1848, Pasteur argued that the two crystal types were made of the same molecules, albeit with different symmetries. When combined in what is now called a racemic mixture, the different molecules canceled each other’s ability to rotate light. As University of Colorado, Denver, historian of science and medicine Joseph Gal writes, Pasteur described his separated samples as “dissymmetric crystals facing one another in a mirror” (Bull. Hist. Chem. 2013, 38, 7).

While French chemistry students are celebrating Pasteur’s chiral wine discovery, researchers half a world away may have given us more excuses to celebrate the grapey beverage.

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Credit: Shutterstock
Wine grapes: Now known to pack 23 more stilbenoids.
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Credit: Shutterstock
Wine grapes: Now known to pack 23 more stilbenoids.

Fear not, this won’t be an account of how resveratrol, a component of red wine, may (or may not) be health promoting. Instead, it’s a promising announcement about the compound’s extended family.

Resveratrol is the most famous member of the stilbenoid family, which has been shown to be heart-friendly, among other things. These stilbenoids are produced by grape vines under a variety of conditions, including when the plants are under microbial attack and when they are pruned.

A team led by Cédric Saucier of the University of British Columbia, in Vancouver, reported this summer that red wine contains some 41 different stilbenoid compounds, 23 of which were previously unknown (Rapid Commun. Mass Spectrom. 2013, DOI: 10.1002/rcm.6636). The discovery may inspire researchers studying red wine’s health effects to expand their work to include some of resveratrol’s lesser known cousins.

Sarah Everts wrote this week’s column. Please send comments and suggestions to newscripts@acs.org.

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