| Formation Routes of Interstellar Glycine Involving Carboxylic Acids: Possible Favoritism Between Gas and Solid Phase. | |
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MedLine Citation:
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PMID: 22066498 Owner: NLM Status: Publisher |
Abstract/OtherAbstract:
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Abstract Despite the extensive search for glycine (NH(2)CH(2)COOH) and other amino acids in molecular clouds associated with star-forming regions, only upper limits have been derived from radio observations. Nevertheless, two of glycine's precursors, formic acid and acetic acid, have been abundantly detected. Although both precursors may lead to glycine formation, the efficiency of reaction depends on their abundance and survival in the presence of a radiation field. These facts could promote some favoritism in the reaction pathways in the gas phase and solid phase (ice). Glycine and these two simplest carboxylic acids are found in many meteorites. Recently, glycine was also observed in cometary samples returned by the Stardust space probe. The goal of this work was to perform theoretical calculations for several interstellar reactions involving the simplest carboxylic acids as well as the carboxyl radical (COOH) in both gas and solid (ice) phase to understand which reactions could be the most favorable to produce glycine in interstellar regions fully illuminated by soft X-rays and UV, such as star-forming regions. The calculations were performed at four different levels for the gas phase (B3LYP/6-31G*, B3LYP/6-31++G**, MP2/6-31G*, and MP2/6-31++G**) and at MP2/6-31++G** level for the solid phase (ice). The current two-body reactions (thermochemical calculation) were combined with previous experimental data on the photodissociation of carboxylic acids to promote possible favoritism for glycine formation in the scenario involving formic and acetic acid in both gas and solid phase. Given that formic acid is destroyed more in the gas phase by soft X-rays than acetic acid is, we suggest that in the gas phase the most favorable reactions are acetic acid with NH or NH(2)OH. Another possible reaction involves NH(2)CH(2) and COOH, one of the most-produced radicals from the photodissociation of acetic acid. In the solid phase, we suggest that the reactions of formic acid with NH(2)CH or NH(2)CH(2)OH are the most favorable from the thermochemical point of view. Key Words: Interstellar molecules?Interstellar environments?Abiotic organic synthesis?Extraterrestrial organic compounds?Prebiotic chemistry. Astrobiology 11, xxx?xxx. |
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Authors:
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Sergio Pilling; Leonardo Baptista; Heloisa M Boechat-Roberty; Diana P P Andrade |
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Publication Detail:
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Type: JOURNAL ARTICLE Date: 2011-11-8 |
Journal Detail:
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Title: Astrobiology Volume: - ISSN: 1557-8070 ISO Abbreviation: - Publication Date: 2011 Nov |
Date Detail:
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Created Date: 2011-11-9 Completed Date: - Revised Date: - |
Medline Journal Info:
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Nlm Unique ID: 101088083 Medline TA: Astrobiology Country: - |
Other Details:
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Languages: ENG Pagination: - Citation Subset: - |
Affiliation:
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1 Universidade do Vale do Para?ba (UNIVAP) , Instituto de Pesquisa e Desenvolvimento, Urbanova, S?o Jos? dos Campos, Brazil . |
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