Recherche de traces de vie extraterrestre : élaboration d'une unité d'extraction et d'analyse chirale pour la séparation énantiomérique in situ de molécules organiques d'intérêt exobiologique

Abstract : Looking for extraterrestrial life, particularly on Mars, has become a challenging aim for future space missions. In this framework, looking for organic molecules and studying their enantiomeric properties could lead to the first clues of an extinct or extant life on this planet. Indeed, life as we know it consists in one of the two specular forms of organic molecules only, and it has been shown that conditions at Mars could preserve, at least partially, this enantiomeric excess. Gas Chromatograph coupled to a Mass Spectrometer (GC-MS) is nowadays the most pertinent space compatible analytical tool for the detection of volatile organics. In order to transform refractory molecules suchas amino acids into volatile ones, we are putting forward a chemical derivatization with dimethylformamidedimethyl-acetal (DMF-DMA). This reaction, when coupled with an analytical step using a chiral chromatographic column, is perfectly adapted to enantiomeric separation within the space constraints. This thesis develops a method of derivatization of the chiral organic molecules with methylation reagent DMFDMA in order to separate and analyze in situ the enantiomers by GC-MS during the future Martian missions. This analytical tool consists in a reaction chamber into which the solid sample is dropped. From this sample, the molecules of interest are successively extracted and derivatized with DMF-DMA to be detected byGC-MS. From a low quantity of Martian analogue soil (50 mg of Atacama soil) and after a complete optimization of each step, numerous molecules of different kinds present at traces levels have been successfully detected, such as amino, carboxylic and nucleic acids. Among these molecules, some of the chiralones have been resolved regarding their enantiomeric forms. The whole procedure is elaborated within the technological and operational limits imposed by a space experiment, each step having been designed to becarried out robotically. Thus, we have developed a complete experiment, sensitive, robust and entirely meeting the requirements of an in situ analysis. That is the reason why this experiment has been selected to be integrated onboard the next Martian mission Exomars 2016/2018 in order to search traces of organic matter at Mars surface and subsurface. Determining an enantiomeric excess, or even homochirality, would be a remarkable breakthrough regarding the presence of an extinct or extant life on the red planet.
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Engineering Sciences [physics]. Ecole Centrale Paris, 2010. French. <NNT : 2010ECAP0033>


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Caroline Freissinet. Recherche de traces de vie extraterrestre : élaboration d'une unité d'extraction et d'analyse chirale pour la séparation énantiomérique in situ de molécules organiques d'intérêt exobiologique. Engineering Sciences [physics]. Ecole Centrale Paris, 2010. French. <NNT : 2010ECAP0033>. <tel-00615481>

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