Searching for amino-acid homochirality on Mars with the Mars Organic Molecule Analyzer (MOMA) onboard ExoMars
Abstract
The joint ESA-Roscosmos Exo-Mars-2018 rover mission plans to seek the signs of a past or a present life on Mars. The Mars Organic Molecule Analyzer (MOMA) experiment onboard theExoMars rover will be a key analytical tool in providing molecular information from Mars solid samples, with a specific focus on the characterization of their organic content. In this purpose, one of MOMA's main instruments is a gas chromatograph-mass spectrometer (GC-MS), which provides a unique ability to characterize a broad range of compounds and allow chemical analyses on volatile and refractory species. The challenge with the analysis of this refractory matter embedded in soil is their primary extraction before their analysis by GC-MS. Since the extraction of organic matter is not possible by liquid solvent extraction, we have developed a method based on the thermodesorption and subsequent derivatization of the organic molecules. The goal of the thermodesorption is to extract the organic matter by heating the sample quickly enough not to degrade its organic content. One of the main focuses is to determine the chirality of this organic matter, notably amino acids. Indeed, on Earth, homochirality of molecules is an indicator for the presence of life. Amino acids appear to bear only the left-handed form (L) in living system. However, other refractory compounds can raise interest: nucleobases, carboxylic acids and PAHs are among molecules supported by life as we know it, and all of them can display chirality. The intrinsic chirality of molecules being thermosensitive, the thermodesorption parameters have been adjusted to occur within a range of temperatures from 150 °C to 300 °C over a period of 30 s to 10 min, depending on the chemical compound. Under these conditions, we have shown that amino acids are not degraded and that their chirality is preserved. Once extracted, refractory molecules with labile hydrogens (e.g. amino acids, nucleobases, carboxylic acids, etc.) are derivatized. Two different derivatization techniques are applied. The first one is a more general but more sensitive derivatization with a silylating reagent, the N,N-methyl-tert-butyl-dimethylsilyl-trifluoroacetamide (MTBSTFA). The derivative compounds are then separated on an RTX-5 (Restek) capillary column. The second derivatization technique implies a methylation reagent, dimethylformamide dimethylacetal (DMF-DMA). This derivatization, combined with an analysis on a chiral capillary column (Chirasil-β-dex), allows the compounds to be resolved regarding their enantiomers. It will be used on MOMA if a chiral analysis of a soil has to be performed. In laboratory, a promising 11 out of the 19 proteinic amino acids can be separated with DMF-DMA derivatization.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2012
- Bibcode:
- 2012AGUFM.P13A1891B
- Keywords:
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- 5200 PLANETARY SCIENCES: ASTROBIOLOGY;
- 5215 PLANETARY SCIENCES: ASTROBIOLOGY / Origin of life