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CD was used in the search for optical activity in extraterrestrial samples, an important key for the study of the origin of life. Microfabricated lab-on-a-chip amino acid analyzer has been developed to check the hypothesis that extraterrestrial life would be based on homochiral amino acid polymers [1]. The hydrolyzed amino acids were labeled with fluorescamine and then analyzed in minutes via a capillary electrophoresis (CE) separation in the presence of HPBCD as the chiral recognition agent. The analyzer was coupled directly with the Mars Organic Detector (MOD-IIII) which was enabled by the nanoliter valves, pumps and reactors.
Mars Organic Analyzer (MOA), a portable analysis system for amino acid extraction based on microchip CE and chiral analysis, a low-volume, high-sensitivity apparatus was tried first for extracts of the Murchison meteorite. Typical limits of detection were ̃ 50 nM. Amino acids were first extracted from soil by sublimation to a cold finger coated with fluorescamine for solid phase labeling. Sample transfer between MOD and the CE device was achieved through a capillary sipper driven by microfabricated valves and pumps. Preliminary chiral analyses of soil extracts from Mars analog sites such as Atacama Desert in Chile have shown amino acid detection down to low ppb concentrations [2].
Later a GC-MS method based on the derivatization of amino acids by using a mixture of perfluorinated alcohols and perfluorinated anhydrides and two different chiral columns a Chirasil-L-Val and a gamma-cyclodextrin Rt- gamma -DEXsa stationary phases has been developed [3]. Linearity studies and the measurement of the limit of detection LOD proved that the proposed method was suitable for a quantitative determination of several amino acids enantiomers
The method was optimized using N,N-dimethylformamide dimethylacetal (DMF-DMA) as derivatizing agent. In order to optimize the chiral derivatization, within space operating conditions, several parameters such as temperature (90 to 170°C) and reaction time (30 sec to 60 min) have been studied using a Chirasil-Dex capillary column (methyl BCD) for the enantiomeric separation. This technique performed in one-step reaction is space compatible and allows to identify 18 out of the 20 proteogenic amino acids and to separate enantiomerically 11 out of the 19 ones (glycine being non-chiral) with a single column using β-cyclodextrin stationary phase. Racemization is all the more important since temperature is the key factor of this phenomenon. The higher the temperature, the faster will the racemization be. Thus, for example when only D-form of threonine is injected, the D-enantiomeric excess drops from 100 to 28 when the temperature used for the derivatisation is increased from 70 to 150°C, this drop being respectively 72 and 60 at 90 and 120°C. The optimal heating time of the derivatization reaction has been also determined allowing high derivatization efficiency and low rate of racemization of the enantiomers and destruction of the amino acids. Quantitative studies were also carried out: linearity studies and the measurement of the limit of detection (LOD) show that the proposed method is suitable for a quantitative determination of enantiomers of several amino acids within a limit of detection (lower than the ppb level) compatible with that found in Martian meteorites.
The European Space Agency’s Rosetta mission was launched in March 2004 in order to reach comet 67P/Churyumov-Gerasimenko by August 2014. The Cometary Sampling and Composition experiment (COSAC) onboard the Rosetta mission’s lander “Philae” (see the featured image) has been designed for the cometary in situ detection and quantification of organic molecules using GC-MS. The GC unit of COSAC was equipped with eight capillary columns with various specific stationary phases for molecular separation. Three of these stationary phases were used to chromatographically resolve enantiomers, as they were composed of liquid polymers of polydimethylsiloxane (PDMS) to which chiral valine or cyclodextrin units were attached. Throughout the ten years of Rosetta’s journey through space to reach comet 67P, these liquid stationary phases have been exposed to space vacuum, as the capillary columns within the COSAC unit were not sealed or filled with carrier gas. Enantiomeric resolution capabilities of these chiral liquid enantioselective stationary phases have not been affected by exposure to space vacuum conditions. Thus it was concluded that the three chiral stationary phases of the COSAC experiment onboard the Rosetta mission lander “Philae” can be considered to have maintained their
resolution capacities throughout their journey prior to cometary landing in November 2014 [5].
Despite of intense preparation and anticipation, the insufficient sample amount obtained for COSAC’s enantioselective GC-MS run after landing on the surface of comet 67P did not yet allow for the identification and resolution of chiral cometary species [6].
References
[1] Skelley, A.M.; Grunthaner, F.J.; Bada, J.L.; Mathies, R.A. Mars Organic Detector III: a versatile instrument for detection of bio-organic signatures on Mars. First Jet Propulsion Laboratory In Situ Instruments Workshop. Edited by Bearman, G.H.; Beauchamp, P.M. Proceedings of the SPIE, 4878, 59-67 (2003). DOI: 10.1117/12.520580
[2] Skelley, A.M.; Grunthaner, F.J.; Bada, J.L.; Mathies, R.A. Sensitive Amino Acid Composition and Chirality Analysis in the Martian Regolith with a Microfabricated in situ Analyzer. American Geophysical Union, Fall Meeting 2003, abstract id.P42C-07. Bibcode: 2003AGUFM.P42C..07S
[3] Zampolli, M.; Sternberg, R.; Szopa, C.; Pietrogrande, M. C.; Buch, A.; Dondi, F.; Raulin, F. GC-MS analysis of amino acid enantiomers as their N(O,S)-perfluoroacyl perfluoroalkyl esters: application to space exploration. 36th COSPAR Scientific Assembly. Held 16 – 23 July 2006, in Beijing, China. Meeting abstract from the CDROM, #1763. Bibcode: 2006cosp…36.1763Z
[4] Freissinet, C.; Buch, A.; Sternberg, R.; Rodier, C.; Garnier, C.; Szopa, C.; Stambouli, M.; Goesmann, F. Looking for clues of extant or extinct life on Mars: GC-MS analysis of amino acid enantiomers using N,N-Dimethylformamide Dimethylacetal (DMF-DMA). European Planetary Science Congress 2008, Proceedings of the conference held 21-25 September, 2008 in Münster, Germany. Online at http://meetings.copernicus.org/epsc2008, p.823. Bibcode: 2008epsc.conf..823F
[5] Meierhenrich, U.J.; Cason, J.R.L.; Szopa, C.; Sternberg, R.; Raulin, F.; Thiemann, W.H.-P.; Goesmann, F. Evaluating the robustness of the enantioselective stationary phases on the Rosetta mission against space vacuum vaporization. Advances in Space Research, 52(12), 2080-2084, 2013. DOI: 10.1016/j.asr.2013.09.018 Bibcode: 2013AdSpR..52.2080M
[6] Ulamec, S.; Goesmann, F.; Meierhenrich, U.J. Philae Landing on Comet 67P/Churyumov-Gerasimenko –Planned Chirality Measurements and Ideas for the Future. J. of Interd. Method. and Issues Sci.: 4, 2018, DOI: 10.18713/JIMIS-230718-4-2