On the Interaction of Adenine with Ionizing Radiation: Mechanistical Studies and Astrobiological Implications

The molecular inventory available on the prebiotic Earth was likely derived from both terrestrial and extraterrestrial sources. A complete description of which extraterrestrial molecules may have seeded early Earth is therefore necessary to fully understand the prebiotic evolution which led to life....

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Bibliographic Details
Published in:The Astrophysical journal 2011-04, Vol.730 (2), p.69-jQuery1323909737395='48'
Main Authors: Evans, Nicholas L, Bennett, Chris J, Ullrich, Susanne, Kaiser, Ralf I
Format: Article
Language:English
Subjects:
ADENINES
AMINES
ANTIMETABOLITES
AROMATICS
Astronomy
ASTROPHYSICS, COSMOLOGY AND ASTRONOMY
AZAARENES
CHARGED PARTICLES
CHEMICAL REACTIONS
CLOUDS
COSMIC RADIATION
DRUGS
Earth, ocean, space
EPOXIDES
Exact sciences and technology
HETEROCYCLIC COMPOUNDS
ICE
IONIZING RADIATIONS
NITRILES
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
ORGANIC OXYGEN COMPOUNDS
PURINES
RADIATIONS
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Summary:The molecular inventory available on the prebiotic Earth was likely derived from both terrestrial and extraterrestrial sources. A complete description of which extraterrestrial molecules may have seeded early Earth is therefore necessary to fully understand the prebiotic evolution which led to life. Galactic cosmic rays (GCRs) are expected to cause both the formation and destruction of important biomolecules--including nucleic acid bases such as adenine--in the interstellar medium within the ices condensed on interstellar grains. The interstellar ultraviolet (UV) component is expected to photochemically degrade gas-phase adenine on a short timescale of only several years. However, the destruction rate is expected to be significantly reduced when adenine is shielded in dense molecular clouds or even within the ices of interstellar grains. Here, biomolecule destruction by the energetic charged particle component of the GCR becomes important as it is not fully attenuated. Presented here are results on the destruction rate of the nucleobase adenine in the solid state at 10 K by energetic electrons, as generated in the track of cosmic ray particles as they penetrate ices. When both UV and energetic charged particle destructive processes are taken into account, the half-life of adenine within dense interstellar clouds is found to be ~6 Myr, which is on the order of a star-forming molecular cloud. We also discuss chemical reaction pathways within the ices to explain the production of observed species, including the formation of nitriles (R-C=N), epoxides (C-O-C), and carbonyl functions (R-C=O).
ISSN:0004-637X
1538-4357
DOI:10.1088/0004-637X/730/2/69