Gas chromatography coupled-to Fourier transform orbitrap mass spectrometer for enantioselective amino acid analyses: Application to pre-cometary organic analog

International audienceGas chromatography (GC) is a separation technique commonly developed for targeted in situ analyses in planetary space missions. It is coupled with low-resolution mass spectrometry to obtain additional structural information and allow compound identification. However, ground-based analyses of extraterrestrial samples have shown the presence of large molecular diversities. For future targeted in situ analyses, it is therefore essential to develop new technologies. High resolution mass spectrometry (HRMS) is currently being spatialized using FT-orbitrap-MS technology. In this contribution, the coupling of gas chromatography with FT-orbitrap-MS is studied for targeted amino acid analyses. The method for enantioselective separation of amino acids was optimized on a standard mixture comprising 47 amino acid enantiomers. Different ionization modes were optimized, chemical ionization with three different reactive gases (NH 3 , CH 4 and NH 3 /CH 4) and electron impact ionization at different electron energies. Single ion and full scan monitoring modes were compared, and detection and quantification limits were estimated by internal calibration under the optimized conditions. The GC-FT-orbitrap-MS demonstrated its ability to separate 47 amino acid enantiomers with minimal co-elution. Furthermore, due to the high mass resolution and accuracy of FT-orbitrap-MS, with mass extraction, the S/N is close to zero, allowing average LOD values of 10⁻ 7 M, orders of magnitude lower than conventional GC-MS techniques. Finally, these conditions were tested for enantioselective analysis of amino acids on an analog of a pre-cometary organic material showing similarities to that of extraterrestrial materials

Polydimethylsiloxane/Additive Systems for Thermal and Ultraviolet Stability in Geostationary Environment

The development of radiation resistant materials is an ongoing challenge for space industry. High-energy irradiation (ultraviolet, electrons, neutrons, protons) induce damage to materials and electronic components in spaceships. Silicone resins are often used and play a key role as coatings and adhesive materials for satellites. Polydimethylsiloxanes show material exhaustion after long-term exposure to ultraviolet irradiation. Consequently, solutions are required to increase their thermo-and photostability under solar irradiation. Three different families of additives, namely ultraviolet absorbers, hindered amine light stabilizers, and a carbazole derivative are investigated. Those ultraviolet stabilizers were mixed with polydimethylsiloxane, then a cross-linking process was run by hydrosilylation. When ultraviolet absorbers could not be used due to a miscibility problem, addition of 0.5 wt % of bis (2,2,6,6-tetramethylpiperidin-4-yl)decanedioate (hindered amine light stabilizer 1) was shown to increase the thermal stability, measured by thermogravimetric analysis, from 360 to 395°C (Td 5%). Using visible near-infrared spectroscopy and after 450 equivalent solar hours of ultraviolet irradiation, an average increase of 2.6% in the ultraviolet stability was also obtained in the wavelength range from 250 to 400 nm. A polydimethylsiloxane/ dibromocarbazole 1.0 wt% did not improve the ultraviolet stability but exhibited a strong increase (about 100°C) of the degradation temperature of the polydimethylsiloxane

Lobular architecture of human adipose tissue defines the niche and fate of progenitor cells

International audienceHuman adipose tissue (hAT) is constituted of structural units termed lobules, the organization of which remains to be defined. Here we report that lobules are composed of two extracellular matrix compartments, i.e., septa and stroma, delineating niches of CD45−/CD34+/CD31− progenitor subsets characterized by MSCA1 (ALPL) and CD271 (NGFR) expression. MSCA1+ adipogenic subset is enriched in stroma while septa contains mainly MSCA1−/CD271− and MSCA1−/CD271 high progenitors. CD271 marks myofibroblast precursors and NGF ligand activation is a molecular relay of TGFβ-induced myofibroblast conversion. In human subcutaneous (SC) and visceral (VS) AT, the progenitor subset repartition is different, modulated by obesity and in favor of adipocyte and myofibroblast fate, respectively. Lobules exhibit depot-specific architecture with marked fibrous septa containing mesothelial-like progenitor cells in VSAT. Thus, the human AT lobule organization in specific progenitor subset domains defines the fat depot intrinsic capacity to remodel and may contribute to obesity-associated cardiometabolic risks