Quantum Tunneling Mediated Low-Temperature Synthesis of Interstellar Hemiacetals

Sugars and sugar-related molecules are ubiquitous in carbonaceous meteorites and in star-forming regions, but the underlying mechanisms of their formation have remained largely elusive. Herein, we report an unconventional synthesis of the hemiacetal, (R/S)-1-methoxyethanol (CH₃OCH(OH)CH₃), through quantum tunneling mediated reactions in low-temperature interstellar model ices composed of acetaldehyde (CH₃CHO) and methanol (CH₃OH). The detection of racemic 1-methoxyethanol through a bottom-up synthesis from simple, abundant precursor molecules within interstellar ices represents a vital starting point to the formation of complex interstellar hemiacetals. Once synthesized, hemiacetals may act as possible precursors to interstellar sugars and sugar-related molecules in deep space.