The physicochemical selection and enrichment of one chiral form over its mirror image isomer (enantiomer) occurred under non-equilibrium conditions. This selection is presumed to be an important step towards the origin of self-organization leading to the emergence of life. Life, as it is known to us, uses exclusively l-amino acid and d-sugar enantiomers for the molecular architecture of proteins and nucleic acids. Therefore, molecular symmetry was broken at some moment of time in the prebiotic world, most probably in a suitable planetary environment. The asymmetric photolysis of extraterrestrial organic matter with circularly polarized light is considered as a possible source of the initial symmetry breaking [1].

Comets and asteroids are interplanetary objects that have preserved a chemical record of the early Solar System at a time when molecular cloud material was abundant in circumstellar disks. In order to gain accesses to the information about the chemical nature of the organic extraterrestrial matter, the Murchison meteorite sample and cometary ice analogues were analysed in our laboratory by two-dimensional gas chromatography (GC×GC). In the Murchison meteorite more than 60 amino acids were identified, while some of them such as β-leucine and several N-alkylated amino acids have never been detected before. Some of the identified chiral amino acids expressed enantiomeric disequilibrium of several %. The following analysis of the organic residues resulting from laboratory simulation of photo/thermo-chemical processes in astrophysical ices allowed for the identification of 10 aldehydes, including the sugar-related glycolaldehyde and glyceraldehyde—two species considered as key prebiotic intermediates in the synthesis of ribonucleotides [2]. These identifications brought a wealth of information on the chemical composition of comets and meteorites, and allowed us proceed to the next step: the asymmetric photochemistry of laboratory organic residues at synchrotron SOLEIL.

In November 2014 five organic residues resulting from H2O:CH3OH:NH3 (12:3.5:1) ice mixtures were separately irradiated at synchrotron SOLEIL with left- and right-handed circularly polarized UV light. The ongoing analysis of photoprocessed residue will provide data on the enantiomeric enrichment of glyceraldehyde. The obtained data will allow us to develop the theory on the role of cpl in creating local enantiomeric disequilibrium.

References

[1] I. Myrgorodska, C. Meinert, Z. Martins et al. Angew Chem Int Ed 2015, 53, 1402-1412.

[2] P. de Marcellus, C. Meinert, I. Myrgorodska et al. PNAS U.S.A. 2015, 112, 965-970.