Urea, Glycolic Acid, and Glycerol in an Organic Residue Produced by Ultraviolet Irradiation of Interstellar/Pre-Cometary Ice Analogs

Abstract

More than 50 stable organic molecules have been detected in the interstellar medium (ISM), from ground-based and onboard-satellite astronomical observations, in the gas and solid phases. Some of these organics may be prebiotic compounds that were delivered to early Earth by comets and meteorites and may have triggered the first chemical reactions involved in the origin of life. Ultraviolet irradiation of ices simulating photoprocesses of cold solid matter in astrophysical environments have shown that photochemistry can lead to the formation of amino acids and related compounds. In this work, we experimentally searched for other organic molecules of prebiotic interest, namely, oxidized acid labile compounds. In a setup that simulates conditions relevant to the ISM and Solar System icy bodies such as comets, a condensed CH(3)OH:NH(3) = 1:1 ice mixture was UV irradiated at approximately 80 K. The molecular constituents of the nonvolatile organic residue that remained at room temperature were separated by capillary gas chromatography and identified by mass spectrometry. Urea, glycolic acid, and glycerol were detected in this residue, as well as hydroxyacetamide, glycerolic acid, and glycerol amide. These organics are interesting target molecules to be searched for in space. Finally, tentative mechanisms of formation for these compounds under interstellar/pre-cometary conditions are proposed.

The Photochemistry of Pyrimidine in Realistic Astrophysical Ices and the Production of Nucleobases

“…These photoproducts are embedded in a residue that is stable at 300 K and can be recovered after the sample is warmed (e.g., Bernstein et al 1995;Muñoz Caro & Schutte 2003). Analysis of these residues reveals that they contain a wide variety of organic compounds including molecules of biological interest such as amino acids, urea, glycerol, and amphiphiles (Dworkin et al 2001;Bernstein et al 2002a;Muñoz Caro et al 2002;Nuevo et al 2008Nuevo et al , 2010. The addition of PAHs to these ices leads to the formation of aromatic molecules that contain a wide range of functional groups on their peripheral carbon atoms (Bernstein et al 1999(Bernstein et al , 2002b.…”

Aldehydes and sugars from evolved precometary ice analogs: Importance of ices in astrochemical and prebiotic evolution

“…Among the numerous individual molecules detected in these residues, hexamethylenetetramine (HMT) is a dominant species (10-13), although it seems not to have any direct prebiotic implication (14). On the other hand, several molecules of potential prebiotic interest have been found, such as amino and diamino acids (14)(15)(16)(17)(18), hydantoin (19), urea and glycolic acid (6,20), lipid precursors (21), quinones when polycyclic aromatic hydrocarbons are irradiated in water ice (22), and even nucleobases-however, only when pyrimidine is added to the initial ice mixture (23)(24)(25). The presence of sugars, in particular those included in nucleotides that are the building blocks of nucleic acids, has never been reported in these residues.…”

On the Plausibility of Pseudosugar Formation in Cometary Ices and Oxygen-rich Tholins

“…The former has been unequivocally identified in comets and the interstellar medium (Hollis et al 2002;Crovisier et al 2004). Likewise, glycerol is present in comets (Briggs et al 1992) and its formation can also be simulated in ice analogs subjected to UV irradiation (Nuevo et al 2010). …”