Interstellar Formation of Biorelevant Pyruvic Acid (CH <sub>3</sub>COCOOH)

Abstract

Pyruvic acid represents a key molecular building block in prebiotic chemistry to form metabolites and amino acids. As conditions on early Earth were not favorable for an endogenous formation of pyruvic acid, an exogenous delivery by comets and meteorites constitutes an appealing alternative. However, despite the detection of more than 200 molecules in interstellar and circumstellar environments, pyruvic acid has yet remained elusive. Here we report on the formation of pyruvic acid by barrierless recombination of hydroxycarbonyl (HOCO) and acetyl (CH3CO) radicals in interstellar ices modelling interstellar conditions of acetaldehyde (CH3CHO) and carbon dioxide (CO2) driven by galactic cosmic rays. Exploiting isotopically labelled ices and photoionization reflectron time-of-flight mass spectrometry, the subliming neutral reaction products were selectively photoionized in the temperature programmed desorption phase and isomers discriminated based on their distinct ionization energies. These results reveal a key reaction pathway for the synthesis of pyruvic acid through non-equilibrium reactions in interstellar ices in cold molecular clouds like TMC-1 and star forming regions such as the Orion Molecular Cloud complex (OMC-1), thus offering a unique entry point to abiotic organic synthesis in deep space.