THE EFFECT OF PLANETARY IMPACT PROCESSING ON AMINO ACID CHIRALITY

Organic molecules found in living organisms exhibit a distinct chiral preference, yet the origin of chirality in biologic systems is an unsolved mystery. The nonracemic amino acids of meteorites provide the only reported natural example of molecular asymmetry measured outside of the biosphere. Did life inherit such asymmetry from these and other prebiotic molecules of extraterrestrial origin?

This presentation will describe laboratory gas gun experiments conducted to test whether amino acids preserve their chirality through the extreme temperature and pressure changes associated with shock processing. A mixture of amino acids, including racemic enantiomers and single enantiomer species, was dissolved in water. Aliquots of this solution were sealed inside stainless steel capsules and subjected to a planar impact by copper projectiles traveling at velocities of 1-1.2 km/s. These velocities, which represent a near-upper limit for our gas gun assembly, correspond to the vertical component of a low angle, terrestrial impact. Pressures generated from shock waves traveling through the capsules were calculated based on impedence matching; temperature histories were calculated using equations of state data for water.

Solutions were characterized by liquid chromatography and mass spectrometry before and after an experiment. While the liquids recovered from the shocked capsules exhibited chemical change with respect to their relative abundance of amino acids, all of the initial amino acid species were still present. We determined that the initial chirality of our amino acids was preserved.