Formation of Glycerol through Hydrogenation of CO ice under Prestellar Core Conditions

TL;DR

This study demonstrates that glycerol, a biologically important molecule, can form on icy dust grains in cold prestellar cores through hydrogenation of CO ice, revealing a potential pathway for prebiotic chemistry in space.

Contribution

It provides experimental evidence for glycerol formation via radical reactions on CO ice, extending known surface chemistry to biologically relevant molecules in space environments.

Findings

Glycerol is formed through radical interactions during CO hydrogenation.

The reaction mechanism suggests potential formation of more complex sugars.

Glyceraldehyde, a related sugar, is tentatively identified.

Abstract

Observational studies reveal that complex organic molecules (COMs) can be found in various objects associated with different star formation stages. The identification of COMs in prestellar cores, i.e., cold environments in which thermally induced chemistry can be excluded and radiolysis is limited by cosmic rays and cosmic ray induced UV-photons, is particularly important as this stage sets up the initial chemical composition from which ultimately stars and planets evolve. Recent laboratory results demonstrate that molecules as complex as glycolaldehyde and ethylene glycol are efficiently formed on icy dust grains via non-energetic atom addition reactions between accreting H atoms and CO molecules, a process that dominates surface chemistry during the 'CO-freeze out stage' in dense cores. In the present study we demonstrate that a similar mechanism results in the formation of the biologically relevant molecule glycerol - HOCH2CH(OH)CH2OH - a three-carbon bearing sugar alcohol necessary for the formation of membranes of modern living cells and organelles. Our experimental results are fully consistent with a suggested reaction scheme in which glycerol is formed along a chain of radical-radical and radical-molecule interactions between various reactive intermediates produced upon hydrogenation of CO ice or its hydrogenation products. The tentative identification of the chemically related simple sugar glyceraldehyde - HOCH2CH(OH)CHO - is discussed as well. These new laboratory findings indicate that the proposed reaction mechanism holds much potential to form even more complex sugar alcohols and simple sugars.