Molecular asymmetry in extraterrestrial organic chemistry: An analytical perspective

Molecular Chirality in Meteorites and Interstellar Ices, and the Chirality Experiment on Board the ESA Cometary Rosetta Mission

“…The chirality of meteoritic amino acids is discussed in detail in Section 2.2. [25] Surprisingly, meteoritic aliphatic amines and carboxylic acids that might share a common chemical origin with amino acids were recently detected as racemates. [24] The ee value varies significantly for different amino acids, as well as for the same amino acid in different meteorite samples, even within the same chondrite.…”

“…[26] Studies of enantiomeric distribution within hydroxycarboxylic acids gave another unexpected result: Lactic acid turned out to be the only hydroxy acid species to display an excess of one enantiomer. [25] 2.2. Such explanations take into account the possible role of ultraviolet circularly polarized light (UV-CPL), [28] deracemization during aqueous altera-tions, [29] and possible asymmetric effects of inorganic matrices within the meteorite, [30] or, alternatively, the complex interplay between compound-specific physicochemical properties, synthetic pathways, and/or so-far unknown symmetry-breaking effects.…”

“…An investigation on the terrestrially rare C 5 -C 7 amino acids in the Murchison meteorite demonstrated nonzero ee values in favor of the l configuration for a-amino-a,bdimethylpentanoic acid, isovaline, norvaline, and a-methylnorvaline, [24,25,33] whereas b-aminobutyric acid was found to be racemic. In contrast to proteinogenic amino acids, which can lose and reacquire their a-hydrogen atom through the attainment of equilibrium during aqueous alteration, adialkylated amino acids are believed to preserve pristine ee values.…”

Discovery of the interstellar chiral molecule propylene oxide (CH 3 CHCH 2 O)

“…The origin of homochirality is a key mystery in the study of our cosmic origins (1). Although homochirality is itself evolutionarily advantageous (2), the mechanism for the selection of one iso-energetic enantiomer over another is uncertain.…”

Looking for the origin of life in Cosmochemistry: Asteroids and their carbon-rich meteorites

“…At first this research was controversial because of the «homochirality» of terrestrial proteins and the ease of terrestrial contamination, but they were eventually detected for some compounds that are abundant in meteorites but not common in terrestrial biochemistry, the a-methyla-amino acids, and excesses of enantiomeric (ee) were observed that, even though they were not as extensive, had the same configuration (L-) as terrestrial amino acids (Pizzarello & Groy, 2011). To date, ten of these compounds and one hydroxy acid have shown to be ee and the findings have raised anew the speculations that extraterrestrial prebiotic processes might have provided the early Earth with a «primordial» inventory of essential organic molecules, giving molecular evolution a push due to their chiral asymmetry, i.e., this has brought about speculation about possible exobiology.…”