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Mechanisms for the Formations of the Thymine Under Astrophysical Conditions and Implications for the Origin of LifeNucleobases are the carriers of the genetic information in ribonucleic acid and deoxyribonucleic acid (DNA) for all life on Earth. Their presence in meteorites clearly indicates that compounds of biological importance can form via non-biological processes in extraterrestrial environments. Recent experimental studies have shown that the pyrimidine-based nucleobases uracil and cytosine can be easily formed from the ultraviolet irradiation of pyrimidine in H2O-rich ice mixtures that simulate astrophysical processes. In contrast, thymine, which is found only in DNA, is more difficult to form under the same experimental conditions, as its formation usually requires a higher photon dose. Earlier quantum chemical studies confirmed that the reaction pathways were favorable provided that several H2O molecules surrounded the reactants. However, the present quantum chemical study shows that the formation of thymine is limited because of the inefficiency of the methylation of pyrimidine and its oxidized derivatives in an H2O ice, as supported by the laboratory studies. Our results constrain the formation of thymine in astrophysical environments and thus the inventory of organic molecules delivered to the early Earth and have implications for the role of thymine and DNA in the origin of life.
Document ID
20170001626
Acquisition Source
Ames Research Center
Document Type
Reprint (Version printed in journal)
External Source(s)
Authors
Bera, Partha P.
(Bay Area Environmental Research Inst. Petaluma, CA, United States)
Nuevo, Michel
(Bay Area Environmental Research Inst. Petaluma, CA, United States)
Materese, Christopher K.
(Bay Area Environmental Research Inst. Petaluma, CA, United States)
Sandford, Scott A.
(NASA Ames Research Center Moffett Field, CA United States)
Lee, Timothy J.
(NASA Ames Research Center Moffett Field, CA United States)
Date Acquired
February 17, 2017
Publication Date
April 12, 2016
Publication Information
Publication: Journal of Chemical Physics
Publisher: AIP
Volume: 144
Issue: 14
ISSN: 0021-9606
e-ISSN: 1089-7690
Subject Category
Exobiology
Report/Patent Number
ARC-E-DAA-TN31885
Funding Number(s)
CONTRACT_GRANT: NNX14AR61A
Distribution Limits
Public
Copyright
Other
Keywords
Origin
Mechanism
Thymine

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