Aldehydes are ubiquitous in star-forming regions and carbonaceous chondrites, serving as essential intermediates in metabolic pathways and molecular mass growth processes to vital biomolecules necessary for the origins of life. However, their interstellar formation mechanisms have remained largely elusive. Here, we unveil the formation of lactaldehyde (CH3CH(OH)CHO) by barrierless recombination of formyl (HĊO) and 1-hydroxyethyl (CH3ĊHOH) radicals in interstellar ice analogs composed of carbon monoxide (CO) and ethanol (CH3CH2OH). Lactaldehyde and its isomers 3-hydroxypropanal (HOCH2CH2CHO), ethyl formate (CH3CH2OCHO), and 1,3-propenediol (HOCH2CHCHOH) are identified in the gas phase utilizing isomer-selective photoionization reflectron time-of-flight mass spectrometry and isotopic substitution studies. These findings reveal fundamental formation pathways for complex, biologically relevant aldehydes through non-equilibrium reactions in interstellar environments. Once synthesized, lactaldehyde can act as a key precursor to critical biomolecules such as sugars, sugar acids, and amino acids in deep space.
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Glyceric acid [HOCH2CH(OH)COOH]—the simplest sugar acid—represents a key molecule in biochemical processes vital for metabolism in living organisms such as glycolysis. Although critically linked to the origins of life and identified in carbonaceous meteorites with abundances comparable to amino acids, the underlying mechanisms of its formation have remained elusive. Here, we report the very first abiotic synthesis of racemic glyceric acid via the barrierless radical-radical reaction of the hydroxycarbonyl radical (HOĊO) with 1,2-dihydroxyethyl (HOĊHCH2OH) radical in low-temperature carbon dioxide (CO2) and ethylene glycol (HOCH2CH2OH) ices. Using isomer-selective vacuum ultraviolet photoionization reflectron time-of-flight mass spectrometry, glyceric acid was identified in the gas phase based on the adiabatic ionization energies and isotopic substitution studies. This work reveals the key reaction pathways for glyceric acid synthesis through nonequilibrium reactions from ubiquitous precursor molecules, advancing our fundamental knowledge of the formation pathways of key biorelevant organics—sugar acids—in deep space.
more » « less- Award ID(s):
- 2103269
- PAR ID:
- 10540345
- Publisher / Repository:
- American Association for the Advancement of Science
- Date Published:
- Journal Name:
- Science Advances
- Volume:
- 10
- Issue:
- 11
- ISSN:
- 2375-2548
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract -
We unravel, for the very first time, the formation pathways of hydroxyacetone (CH 3 COCH 2 OH), methyl acetate (CH 3 COOCH 3 ), and 3-hydroxypropanal (HCOCH 2 CH 2 OH), as well as their enol tautomers within mixed ices of methanol (CH 3 OH) and acetaldehyde (CH 3 CHO) analogous to interstellar ices in the ISM exposed to ionizing radiation at ultralow temperatures of 5 K. Exploiting photoionization reflectron time-of-flight mass spectrometry (PI-ReToF-MS) and isotopically labeled ices, the reaction products were selectively photoionized allowing for isomer discrimination during the temperature-programmed desorption phase. Based on the distinct mass-to-charge ratios and ionization energies of the identified species, we reveal the formation pathways of hydroxyacetone (CH 3 COCH 2 OH), methyl acetate (CH 3 COOCH 3 ), and 3-hydroxypropanal (HCOCH 2 CH 2 OH) via radical–radical recombination reactions and of their enol tautomers (prop-1-ene-1,2-diol (CH 3 C(OH)CHOH), prop-2-ene-1,2-diol (CH 2 C(OH)CH 2 OH), 1-methoxyethen-1-ol (CH 3 OC(OH)CH 2 ) and prop-1-ene-1,3-diol (HOCH 2 CHCHOH)) via keto-enol tautomerization. To the best of our knowledge, 1-methoxyethen-1-ol (CH 3 OC(OH)CH 2 ) and prop-1-ene-1,3-diol (HOCH 2 CHCHOH) are experimentally identified for the first time. Our findings help to constrain the formation mechanism of hydroxyacetone and methyl acetate detected within star-forming regions and suggest that the hitherto astronomically unobserved isomer 3-hydroxypropanal and its enol tautomers represent promising candidates for future astronomical searches. These enol tautomers may contribute to the molecular synthesis of biologically relevant molecules in deep space due to their nucleophilic character and high reactivity.more » « less
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Abstract The formation of complex organic molecules by simulated secondary electrons generated in the track of galactic cosmic rays was investigated in interstellar ice analogs composed of methanol and carbon dioxide. The processed ices were subjected to temperature-programmed desorption to mimic the transition of a cold molecular cloud to a warmer star-forming region. Reaction products were detected as they sublime using photoionization reflectron time-of-flight mass spectrometry. By employing isotopic labeling, tunable photoionization and computed adiabatic ionization energies isomers of C2H4O3were investigated. Product molecules carbonic acid monomethyl ester (CH3OCOOH) and glycolic acid (HOCH2COOH) were identified. The abundance of the reactants detected in analog interstellar ices and the low irradiation dose necessary to form these products indicates that these molecules are exemplary candidates for interstellar detection. Molecules sharing a tautomeric relationship with glycolic acid, dihydroxyacetaldehyde ((OH)2CCHO), and the enol ethenetriol (HOCHC(OH)2), were not found to form despite ices being subjected to conditions that have successfully produced tautomerization in other ice analog systems.
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Methylamine (CH 3 NH 2 ) and methanimine (CH 2 NH) represent essential building blocks in the formation of amino acids in interstellar and cometary ices. In our study, by exploiting isomer selective detection of the reaction products via photoionization coupled with reflectron time of flight mass spectrometry (Re-TOF-MS), we elucidate the formation of methanimine and ethylenediamine (NH 2 CH 2 CH 2 NH 2 ) in methylamine ices exposed to energetic electrons as a proxy for secondary electrons generated by energetic cosmic rays penetrating interstellar and cometary ices. Interestingly, the two products methanimine and ethylenediamine are isoelectronic to formaldehyde (H 2 CO) and ethylene glycol (HOCH 2 CH 2 OH), respectively. Their formation has been confirmed in interstellar ice analogs consisting of methanol (CH 3 OH) which is ioselectronic to methylamine. Both oxygen-bearing species formed in methanol have been detected in the interstellar medium (ISM), while for methanimine and ethylenediamine only methanimine has been identified so far. In comparison with the methanol ice products and our experimental findings, we predict that ethylenediamine should be detectable in these astronomical sources, where methylamine and methanimine are present.more » « less
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Abstract The products of the Cl‐atom‐initiated oxidation of hydroxyacetone (HYAC, CH3C(O)CH2OH) have been examined under conditions relevant to the earth's lower atmosphere. Over the range of temperatures studied (252‐298 K), in the absence of NOx, methylglyoxal (CH3C(=O)CH=O, MGLY) was formed with a primary yield >84% (96 ± 9% at 298 K), while in the presence of elevated NOx, MGLY and formic acid were both formed as major primary products. In contrast to a previous study, acetic acid was not identified as a major primary product under the conditions studied. The results are quantitatively interpreted from a consideration of the formation of a stabilized CH3C(O)CH(OH)OO• radical, either in a ≈50% yield from the addition of O2to CH3C(O)CH•(OH) or in 100% yield from the addition of HO2to MGLY. At high temperature and low NOx, decomposition of the stabilized CH3C(O)CH(OH)OO• radical to MGLY is favored, while lower temperatures and conditions of high NOxfavor bimolecular reactions of the stabilized radical, with subsequent production of formic acid. Analysis of the data allows for a semiquantitative determination of
K 3 = (2.9 ± 0.4) × 10−16cm3molecule−1, for the HO2+ MGLY ↔ CH3C(O)CH(OH)OO• equilibrium process at 298 K and a roughly order of magnitude increase inK 3at 252 K.
