Interstellar Formation of 1,2-Propanediol (CH3CH(OH)CH2OH) and 1,2-Ethenediol (HOCHCHOH) — Key Precursors to Sugars and Sugar Derivatives

Although sugars and sugar derivatives—molecules critical to the origins of life—have been identified in carbonaceous meteorites with total abundances typically higher than that of amino acids, their underlying formation mechanisms in interstellar environments remain poorly understood. This study reports the first formation of 1,2-propanediol (CH₃CH(OH)CH₂OH) and 1,2-ethenediol (HOCHCHOH) in low-temperature model interstellar ices composed of methane (CH₄) and ethylene glycol (HOCH₂CH₂OH). 1,2-Propanediol forms via the barrierless radical−radical recombination of the methyl (ĊH₃) with the 1,2-dihydroxyethyl (HOĊHCH₂OH), while 1,2-ethenediol is produced through the decomposition of ethylene glycol. Utilizing vacuum ultraviolet photoionization reflectron time-of-flight mass spectrometry and isotopic substitution experiments, 1,2-propanediol and its isomer 2-methoxyethanol (CH₃OCH₂CH₂OH), along with enols 1,2-ethenediol and vinyl alcohol (CH₂CHOH) were identified in the gas phase during temperature-programmed desorption based on their adiabatic ionization energies and mass-to-charge ratios. Among these compounds, only 1,2-propanediol has not yet been observed in the interstellar medium; these results suggest that it is a promising target for future astronomical detection. Our findings reveal viable abiotic pathways for the formation of biorelevant 1,2-propanediol and 1,2-ethenediol via non-equilibrium chemistry in ethylene glycol-containing interstellar ices, advancing our understanding of the fundamental formation mechanisms of sugars and sugar derivatives in deep space.