A Reflectron Time-of-Flight Mass Spectrometric Study on the Degradation Pathways of Glycine on Mars in the Presence of Perchlorates and Ionizing Radiation

Abstract

The absence of abundant organics on the Martian surface is a much discussed observation. So far, no explanation is completely satisfactory. In this study we aim for a deeper understanding of the degradation processes of organics in the presence of perchlorates that can take place on the Martian surface. Our primary goal is to study the radiation-induced decomposition process of glycine (H2NCH2COOH) in the absence and presence of an oxidizer relevant to the Martian surface—perchlorate anions ( ClO 4 − ) . Glycine and various samples of glycine-1-13C (+H3NC H 2 13 COO−)–magnesium perchlorate hexahydrate (Mg(ClO4)2 · 6H2O) were exposed to energetic electrons mimicking secondary electrons originating from the interaction of galactic cosmic rays (GCRs) with the Martian regolith. Using isotope-labeled and deuterated pure glycine samples such as glycine-1-13C, glycine-d5 (+D3NCD2COO−), glycine-N,N,N-d3 (+D3NCH2COO−), and glycine-2,2-d2 (+H3NCD2COO−), we can conclude that decarboxylation (carbon dioxide loss) of the glycine molecule is exclusively the first decay step during irradiation regardless of whether perchlorate anions are present or not. In pure glycine samples, the decarboxylation co-product methylamine (CH3NH2) and its radiolytic decay product ammonia could both be detected explicitly for the first time. In the presence of perchlorates, (partial) oxidation of the glycine decarboxylation product CH3NH2 may occur. Because the decarboxylation is an equilibrium reaction and the CH3NH2 is effectively removed from the system by this oxidation, glycine cannot be recycled. Therefore the depletion of the CH3NH2 facilitates the process, resulting in an overall 10-fold increase in the formation rate of carbon dioxide and its elevated concentrations in the perchlorate-containing irradiated samples.

Degradation of Adenine on the Martian Surface in the Presence of Perchlorates and Ionizing Radiation: A Reflectron Time-of-flight Mass Spectrometric Study

“…A weak shoulder is also detectable at 1289 cm −1 caused by the second harmonic of the antisymmetric bending vibration of the perchlorate unit ( b -2 ClO as 4 ). The position and shape of the perchlorate vibrational band also agrees well with our previous results (Góbi et al 2016a(Góbi et al , 2016b(Góbi et al , 2017. It is worth noting that multiple vibrational modes of the adenine (C 5 H 5 N 5 ) molecule overlap with this particularly intense band of the perchlorate unit -( ) ClO 4 ; these are the stretching vibrations of the C-N molecules in the five-membered ring (ν CN (R5)), the bending motions of C-H (β C(8)H) and N-H (β N(9)H) moieties, the rocking of the -NH 2 group (ρ NH 2 ), and the wagging of a C-H bond (ω C(2)H).…”

“…Fully detailed discussion of the PI-ReTOF-MS technique, the VUV laser generation by four-wave mixing, and applicability of this method to astrophysically relevant samples can be found in previous papers presented by our group (Maity et al 2014;Abplanalp et al 2015, see also their Supplementary Information and Appendix). PI-ReTOF-MS measurements of Mars-relevant samples were discussed in Góbi et al (2017).…”

“…Increased formation rates of oxidized products such as carbon dioxide (CO 2 ) confirmed the conclusion that the active oxygen originating from radiolysis of perchlorate -( ) ClO 4 accounts for the elevated rates of decomposition as well. Furthermore, the detailed decomposition mechanism of glycine and the effect of the organics-perchlorate ratio were studied in a recent paper utilizing the PI-ReTOF-MS method (Góbi et al 2017). Although these previous works unraveled the detailed mechanisms on the destruction of the simplest amino acidglycine (H 2 NCH 2 COOH)-on Mars, the destruction of nucleobases in the presence of an oxidizer under conditions prevalent in Mars have never been investigated so far.…”

A Vacuum Ultraviolet Photoionization Study on the Formation of N-methyl Formamide (HCONHCH3) in Deep Space: A Potential Interstellar Molecule with a Peptide Bond

“…In order to record and monitor the VUV light, a detection system consisting of a Faraday cup and a diode calibrated by the National Institute of Standards and Technology (NIST) is placed behind the detection region. This tunable VUV photon source allows soft-ionization of molecules with ideally no fragmentation (Förstel et al 2015(Förstel et al , 2016a(Förstel et al , 2016dAbplanalp & Kaiser 2017;Góbi et al 2017). In this work we used a mixture of rhodamine610 and rhodamine640 in the first dye laser, pumped by 532nm, to generate 606.948nm, which is frequency-tripled to ω 1 =202.316nm for the twophoton resonance of krypton (Kr).…”

On the formation and the isomer specific detection of methylacetylene (CH3CCH), propene (CH3CHCH2), cyclopropane (c-C3H6), vinylacetylene (CH2CHCCH), and 1,3-butadiene (CH2CHCHCH2) from interstellar methane ice analogues

“…All experiments were completed in an ultrahigh vacuum (UHV) chamber at pressures of typically 3 Â 10 À11 Torr. 68,84,85 A UHV compatible closed-cycle helium compressor (Sumitomo Heavy Fig. 1 Infrared spectra at 5000-500 cm À1 of several pure unprocessed ices at 5 K. The left inset is a 16Â magnification of 5000-3500 cm À1 and the right inset is a 4Â magnification of 1500-500 cm À1 .…”