Deciphering the origins of life’s asymmetry: The search for biosignatures in space

The preference for l-amino acids in proteins and d-sugars in nucleic acids is a key feature of life. The origin and evolution of biological homochirality still remains unresolved. Abiotic l-enrichments of amino acids in carbonaceous chondrites provide a strong hint that life’s homochirality originated beyond Earth.¹ This, however, hinders the identification of chiral biosignatures of putative past life in current and future space missions. Would a detection of a set of enantioenriched amino acids on Mars, for example, point to traces of extinct life blurred by years of racemisation, or would it merely be a product of abiotic physico-chemistry operating in harsh extra-terrestrial environments? Understanding the origin of small chiral imbalances in solar system bodies and the amplification to life’s homochirality will aid in answering these questions. To date, stellar ultraviolet circularly polarized light (UV CPL) has been recognized as one of the promising candidates for triggering symmetry breaking in interstellar environments.² Monochromatic UV CPL has proven capable of inducing enantiomeric excesses in amino acids via asymmetric photolysis,^3-5 as predicted by their anisotropy spectra. While these are important proof of concept experiments to validate the astrophysical CPL scenario, comparisons of the net effect of broadband CPL with the results of enantioselective analyses of extra-terrestrial samples are necessary. I will outline how a strategic selection of analytes can provide useful insights into the CPL scenario and the origins of chiral biases in extra-terrestrial samples. Here, our latest results on isovaline will be presented,⁶ which ultimately provide a sound explanation for its varying enantiomeric excesses detected in carbonaceous chondrites that have been extensively discussed in the origin-of-life research community over the last two decades. Given their relatively high recalcitrance and resistance to degradation, lipids are one of the best candidate biomarkers in exobiology.⁷ Our recently recorded anisotropy spectra of membrane lipids and their chiral backbones⁸ provide guidelines for future enantioselective analyses of interstellar ice analogues, meteorites and return samples, in particular from Hayabusa2 and OSIRIS-REx missions, the Mars Sample Return Campaign, as well as for the search for traces of life in space by the ExoMars 2028 and Martian Moons eXploration missions.

[1] Glavin, D. P.; Burton, A. S.; Elsila, J. E.; Aponte, J. C.; Dworkin, J. P.  Chem. Rev. 2020, 120, 4660.

[2] Garcia, A. D.; Meinert, C.; Sugahara, H.; Jones, N. C.; Hoffmann, S. V.; Meierhenrich, U. J. Life 2019 9, 29.

[3] Flores, J. J.; Bonner, W. A.; Massey, G. A. J. Am. Chem. Soc. 1977, 99, 3622.

[4] Meinert, C.; Hoffmann, S. V.; Cassam-Chenaï, P.; Evans, A. C.; Giri, C.; Nahon, L.; Meierhenrich, U. J. Angew. Chem. Int. Ed. 2014, 53, 210.

[5] Modica, P.; Meinert, C.; de Marcellus, P.; Nahon, L.; Meierhenrich, U. J.; d'Hendecourt, L. L. S. Astrophys. J. 2014, 788, 79.

[6] Bocková, J.; Jones, N. C.; Topin, J.; Hoffmann, S. V.; Meinert. C. Nat. Commun. 2023, 14, 3381.

[7] Bocková, J.; Jones, N. C.; Hoffmann, S. V.; Meinert. C. Nat. Rev. Chem. 2024, accepted.

[8] Bocková, J.; Garcia A. D.; Jones, N. C.; Hoffmann, S. V.; Meinert. C. Chirality 2024, 36, e23654.

 

Acknowledgement

Supported by the European Research Council under the European Union’s Horizon 2020 research and innovation programme [grant agreement 804144].