New Test Boosts Search for Extraterrestrial Life (Forwarded)

Research News & Publications Office
Georgia Institute of Technology
Atlanta, Georgia

Media Relations Contacts:
Jane Sanders, 404-894-2214
John Toon, 404-894-6986

Technical Contacts:
Tracey Thaler, 404-385-3089 or 404-388-5974
Andreas Bommarius, 404-385-1334

Writer: T.J. Becker

March 30, 2006

New Test Boosts Search for Extraterrestrial Life

Novel chemical reaction could serve as marker for life and simplify space
instrumentation

Atlanta -- Researchers have identified a new test case that could be used
for evaluating extraterrestrial samples for evidence of life. The new test
could ultimately allow the use of simpler analytical instrumentation on
future space missions.

In the search for life on other planets, astrobiologists regard liquid
water and chiral biomolecules to be critical components. "Yet because
chiral molecules can be made synthetically as well as biologically, it's
not enough to just find them on other planets. We need to show a change of
chirality over time," said Tracey Thaler, a graduate student at Georgia
Tech's School of Chemistry and Biochemistry. Thaler works with Professor
Andreas Bommarius in the School of Chemical and Biomolecular Engineering.

Thaler has investigated racemization -- the conversion of an optically
active compound to a racemic form, which has no optical rotation -- as a
new approach for analyzing samples in outer space. "Because this type of
reaction is found only in biological systems, it could serve as a marker
for extraterrestrial life," Thaler explained. She presented results from
the study on Thursday, March 30, at the 231st American Chemical Society
National Meeting in Atlanta.

The study is part of a collaborative effort with Professor Rick Trebino's
research group in Georgia Tech's School of Physics. The two research
groups are trying to improve analytical instruments used on space
missions, research that is sponsored by NASA.

Chromatography, the current method used to evaluate extraterrestrial
samples on space missions, is a tedious process, Bommarius explained.
Another drawback, researchers must know in advance the specific compounds
they're looking for, which isn't always possible. In contrast,
polarimetry, a method for measuring optical activity, does not require
knowledge of the structure being analyzed. But because existing
polarimeters have performance limitations, Georgia Tech researchers are
developing a more sensitive polarimeter that can detect smaller
concentrations of optically active compounds. Thaler's work serves as a
test bed for such an instrument.

"Tracey's study is significant because it marks the first time that
racemization has been looked on as a sign of life on other planets,"
Bommarius said. "What's more, she has identified two new media in which
the enzyme mandelate racemase is active."

Mandelate racemase (MR) is an enzyme that catalyzes the racemization
reaction for the substrate mandelic acid. Mandelate is one the simplest
chiral molecules and has a large specific optical rotation, making it
well-suited for polarization analysis, Thaler explained.

An important part of the study was to determine if MR reactivity could
occur at subzero temperatures found on planets like Mars or moons like
Titan, Europa or Enceladus, where recent data shows water is likely to
exist.

After a number of unsuccessful attempts with organic cryosolvents -- the
most common medium to probe enzyme activity at low temperatures -- Thaler
achieved MR reactivity in two unconventional media. They were concentrated
ammonium salt solutions and water-in-oil microemulsions (anionic
surfactant Aerosol OT and non-ionic surfactant Triton X-100). Racemization
occurred in temperatures as low as -30 degrees Celsius. This was promising
because both the microemulsions and the concentrated salt solutions are
expected to form on other planets and moons.

Another auspicious finding: Measurements for the activation parameters
(thermodynamics) in the ammonium salt solutions and water-in-oil
microemulsions were very similar. "This tells us that racemization is not
only possible in other media, but thermodynamic parameters found in these
media are similar to those found in media that's normally used," Thaler
said.

The next step will be to use the MR system with the new polarimeter being
developed by Trebino's group while Thaler and other members of Bommarius'
team explore additional enzyme systems that might also be good test
models.

Related Links

* School of Chemistry and Biochemistry
http://www.chemistry.gatech.edu/
* School of Chemical and Biomolecular Engineering
http://www.che.gatech.edu/
* Andreas Bommarius
http://www.che.gatech.edu/fac_staff/.../bommarius.php