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Photochemistry of Pyrimidine in Astrophysical Ices: Formation of Nucleobases and Other Prebiotic SpeciesNucleobases are N-heterocycles that are the informational subunits of DNA and RNA. They are divided into two molecular groups: pyrimidine bases (uracil, cytosine, and thymine) and purine bases (adenine and guanine). Nucleobases have been detected in meteorites, and their extraterrestrial origin confirmed by isotopic measurements. Although no N-heterocycles have ever been observed in the ISM, the positions of the 6.2- m interstellar emission features suggest a population of such molecules is likely to be present. However, laboratory experiments have shown that the ultraviolet (UV) irradiation of pyrimidine in ices of astrophysical relevance such as H2O, NH3, CH3OH, CH4, CO, or combinations of these at low temperature (less than or equal to 20 K) leads to the formation of several pyrimidine derivatives including the nucleobases uracil and cytosine, as well as precursors such as 4(3H)-pyrimidone and 4-aminopyrimidine. Quantum calculations on the formation of 4(3H)-pyrimidone and uracil from the irradiation of pyrimidine in pure H2O ices are in agreement with their experimental formation pathways.10 In those residues, other species of prebiotic interest such as urea as well as the amino acids glycine and alanine could also be identified. However, only very small amounts of pyrimidine derivatives containing CH3 groups could be detected, suggesting that the addition of methyl groups to pyrimidine is not an efficient process. For this reason, the nucleobase thymine was not observed in any of the samples. In this work, we study the formation of nucleobases and other photo-products of prebiotic interest from the UV irradiation of pyrimidine in ices containing H2O, NH3, CH3OH, and CO, mixed in astrophysical proportions.
Document ID
20120016602
Acquisition Source
Ames Research Center
Document Type
Conference Paper
Authors
Nuevo, Michel (Search for Extraterrestrial Intelligence Inst. Mountain View, CA, United States)
Sandford, Scott A. (Search for Extraterrestrial Intelligence Inst. Mountain View, CA, United States)
Materese, Christopher K. (Search for Extraterrestrial Intelligence Inst. Moffett Field, CA, United States)
Milam, Stefanie N. (NASA Goddard Space Flight Center Greenbelt, MD, United States)
Date Acquired
August 26, 2013
Publication Date
April 16, 2012
Subject Category
Astrophysics
Report/Patent Number
ARC-E-DAA-TN5082
Meeting Information
Meeting: AbSciCon (Astrobiology Science Conference)
Location: Atlanta, GA
Country: United States
Start Date: April 16, 2012
Funding Number(s)
WBS: WBS 811073.02.07.02.54
CONTRACT_GRANT: NNX10AQ70A
Distribution Limits
Public
Copyright
Public Use Permitted.

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