An official website of the United States government
Abstract Oxygen-containing complex organic molecules are key precursors to biorelevant compounds fundamental for the origins of life. However, the untangling of their interstellar formation mechanisms has just scratched the surface, especially for oxygen-containing cyclic molecules. Here, we present the first laboratory simulation experiments featuring the formation of all three C2H4O isomers—ethylene oxide (c–C2H4O), acetaldehyde (CH3CHO), and vinyl alcohol (CH2CHOH)—in low-temperature model interstellar ices composed of carbon monoxide (CO) and ethanol (C2H5OH). Ice mixtures were exposed to galactic cosmic-ray proxies with an irradiation dose equivalent to a cold molecular cloud aged (7 ± 2) × 105yr. These biorelevant species were detected in the gas phase through isomer-selective photoionization reflectron time-of-flight mass spectrometry during temperature-programmed desorption. Isotopic labeling experiments reveal that ethylene oxide is produced from ethanol alone, providing the first experimental evidence to support the hypothesis that ethanol serves as a precursor to the prototype epoxide in interstellar ices. These findings reveal feasible pathways for the formation of all three C2H4O isomers in ethanol-rich interstellar ices, offering valuable constraints on astrochemical models for their formation. Our results suggest that ethanol is a critical precursor to C2H4O isomers in interstellar environments, representing a critical step toward unraveling the formation mechanisms of oxygen-containing cyclic molecules, aldehydes, and their enol tautomers from alcohols in interstellar ices.
more »
« less
This content will become publicly available on July 10, 2027
Interstellar Ice Chemistry Yields Elusive Sulfinothioic Acid (HS(O)SH)
ABSTRACT Low‐oxidation‐state sulfur oxyacids are key yet experimentally elusive intermediates in interstellar sulfur chemistry; even the simplest member, sulfinothioic acid (HS(O)SH), has neither been detected in space nor isolated terrestrially. The S–S(O) motif, also present in biological systems, can be reduced to form disulfide bridges (RSSR’), suggesting potential astrobiological relevance. Here, we report the first formation of sulfinothioic acid in astrophysically relevant sulfur dioxide (SO2)–water (H2O) ices and its identification via isomer‐selective photoionization reflectron time‐of‐flight mass spectrometry combined with isotopic labeling. Irradiation of these ices at 5 K under ultrahigh vacuum with galactic cosmic‐ray proxies yields sulfinothioic acid. These results establish a missing link in interstellar sulfur chemistry and reveal a previously unrecognized class of astrochemically accessible sulfur oxyacids formed via radical‐mediated, non‐equilibrium processes driven by energetic particles in cold interstellar environments.
more »
« less
- Award ID(s):
- 2407815
- PAR ID:
- 10708648
- Publisher / Repository:
- Wiley-VCH
- Date Published:
- Journal Name:
- Angewandte Chemie International Edition
- ISSN:
- 1433-7851
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Abstract For the last century, the source of sulfur in Earth’s very first organisms has remained a fundamental, unsolved enigma. While sulfates and their organic derivatives with sulfur in the S(+VI) oxidation state represent core nutrients in contemporary biochemistry, the limited bioavailability of sulfates during Earth’s early Archean period proposed that more soluble S(+IV) compounds served as the initial source of sulfur for the first terrestrial microorganisms. Here, we reveal via laboratory simulation experiments that the three simplest alkylsulfonic acids—water soluble organic S(+IV) compounds—can be efficiently produced in interstellar, sulfur-doped ices through interaction with galactic cosmic rays. This discovery opens a previously elusive path into the synthesis of vital astrobiological significance and untangles fundamental mechanisms of a facile preparation of sulfur-containing, biorelevant organics in extraterrestrial ices; these molecules can be eventually incorporated into comets and asteroids before their delivery and detection on Earth such as in the Murchison, Tagish Lake, and Allende meteorites along with the carbonaceous asteroid Ryugu.more » « less
-
Abstract Enols—tautomers of ketones or aldehydes—are considered key intermediates in the formation of prebiotic sugars and sugar acids. Although laboratory simulation experiments suggest that enols should be ubiquitous in the interstellar medium, the underlying formation mechanisms of enols in interstellar environments are largely elusive. Here, we present the laboratory experiments on the formation of glyoxal (HCOCHO) along with its ynol tautomer acetylenediol (HOCCOH) in interstellar ice analogs composed of carbon monoxide (CO) and water (H2O) upon exposure to energetic electrons as a proxy for secondary electrons generated from Galactic cosmic rays. Utilizing tunable vacuum ultraviolet photoionization reflectron time-of-flight mass spectrometry, glyoxal and acetylenediol were detected in the gas phase during temperature-programmed desorption. Our results reveal the formation pathways of glyoxal via radical–radical recombination of two formyl (HĊO) radicals, and that of acetylenediol via keto-enol-ynol tautomerization. Due to the abundance of carbon monoxide and water in interstellar ices, glyoxal and acetylenediol are suitable candidates for future astronomical searches. Furthermore, the detection of acetylenediol in astrophysically relevant ices advances our understanding for the formation pathways of high-energy tautomers such as enols in deep space.more » « less
-
Abstract Sulfur is one of the most abundant elements in the interstellar medium (ISM) and a key component for life, yet little is understood about its chemistry in the ISM. While increasingly larger molecules containing sulfur and oxygen are being observed in the ISM, the largest organic molecule containing oxygen and sulfur, monothioformic acid (HC(O)SH), was only recently detected. There is still no identification of a complex organic molecule (COM, carbon-bearing molecule with six or more atoms) containing both oxygen- and sulfur-bearing functional groups. We extended the laboratory rotational spectrum of 2-mercaptoethanol (HSCH2CH2OH), one of the simplest saturated COMs containing both oxygen and sulfur, into millimeter/submillimeter wavelengths, providing an improved spectral catalog at frequencies required for its interstellar identification. Millimeter/submillimeter transitions were measured for 2-mercaptoethanol from ∼82 to 450 GHz. Using the resulting spectral catalog, we searched for its rotational emission toward the Galactic Center molecular cloud G+0.693-0.027, the high-mass star-forming region Sgr B2(N), the cold dark core TMC-1, the hot core in Orion, and toward the hot corino surrounding the low-mass protostar IRAS 16293-2422B. An extensive analysis of 8584 transitions of 2-mercaptoethanol with = 104, and = 64 is provided. The resulting fit includes a full set of quartic, sextic, and octic distortion constants. We report the nondetection of 2-mercaptoethanol and provide column density upper limits toward each source. While our interstellar search for 2-mercaptoethanol did not result in a detection, the upper limits on its column density provide important constraints for chemical models on the formation of oxygen- and sulfur-bearing COMs.more » « less
-
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 C 2 H 4 O 3 were investigated. Product molecules carbonic acid monomethyl ester (CH 3 OCOOH) and glycolic acid (HOCH 2 COOH) 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) 2 CCHO), 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.more » « less
