Astrochemistry Prefers the Biomolecule: Isomer-Selective Production of Ethanolamine (HOCH2CH2NH2) in Interstellar Model Ices

Abstract

A crucial molecule in the chemistry of life, ethanolamine (HOCH₂CH₂NH₂) is among the most prevalent biomolecules. It serves as a ubiquitous hydrophilic head group for the molecules comprising cellular membranes and it functions as both precursor and intermediate in the biological synthesis of neurotransmitters among other metabolites, protein folding, and posttranslational modification. Because of the out-sized biological importance of this molecule ethanolamine is expected to serve as a signature for prebiotic chemistry in space, highlighting the importance of its recent discovery. Here, we show that model interstellar ices containing methanol (CH₃OH) and methylamine (CH₃NH₂) produce ethanolamine upon exposure to an environment simulating that of dense interstellar molecular clouds. Ethanolamine was identified in the gas phase during temperature-programmed desorption utilizing vacuum ultraviolet photoionization reflectron time-of-flight mass spectrometry. Despite irradiation by electrons with energy far exceeding any covalent interaction, reactions toward C2H7NO isomers are selective for ethanolamine while its isomers are not detected. Computations provide support that polar solvation destabilizes nitrogen- and oxygen-centered radicals while lowering the barrier to intramolecular hydrogen transfer, resulting in the selective stabilization and formation of carbon-centered radicals. These findings explain the unexpected abundance of ethanolamine in the interstellar medium, and the apparent isomer-selectivity of this reaction may represent a mechanism by which ice-phase astrochemical reactions are preferential toward the building blocks of life.