Exploring the link between molecular cloud ices and chondritic organic matter in laboratory

Carbonaceous meteorites are fragments of asteroids rich in organic material. In the forming solar nebula, parent bodies may have accreted organic materials resulting from the evolution of icy grains observed in dense molecular clouds. The major issues of this scenario are the secondary processes having occurred on asteroids, which may have modified the accreted matter. Here, we explore the evolution of organic analogs of protostellar/protoplanetary disk material once accreted and submitted to aqueous alteration at 150 °C. The evolution of molecular compounds during up to 100 days is monitored by high resolution mass spectrometry. We report significant evolution of the molecular families, with the decreases of H/C and N/C ratios. We find that the post-aqueous products share compositional similarities with the soluble organic matter of the Murchison meteorite. These results give a comprehensive scenario of the possible link between carbonaceous meteorites and ices of dense molecular clouds.

The stability of pyridine upon chemical attack under the conditions of primitive Earth

<p>Pyridine is a heterocyclic aromatic molecule of gross formula C<sub>5</sub>H<sub>5</sub>N where the N atom is included in the aromatic ring. The molecule as such is not abundant in nature, but its derivatives are often part of important biomolecules. For instance, it is one of the basic units in the nicotinamide adenine dinucleotide, NADH, which is an essential reducing agent in various biological processes. Interestingly, pyridine derivatives (e.g. 2,4,6-trimethylpyridine and pyridine carboxylic acids) were identified in carbonaceous chondrites [1-4] along with many other molecules of biological significance. In addition to that, nicotinonitrile (3-cyanopyridine) as well as 2- and 4-cyanopyridine have been synthesized in a version of the Miller experiment by the action of electric discharges on ethylene and ammonia, with an intermediate step being the synthesis of pyridine [5]. The possibility that nicotinonitrile hydrolyzed in the primitive ocean to nicotinamide and nicotinic acid reinforces the prebiotic potential of pyridine.</p> <p>In conclusion, either formed locally on Earth from simple precursors or brought by extraterrestrial carriers, the presence of pyridine or of one of its derivatives could have played an important role in the organic chemistry that triggered the origin of life on Earth. Pyridine formation can also be seen as an intermediate step towards the formation of pyrimidine (C<sub>4</sub>H<sub>4</sub>N<sub>2</sub>), a species constituting the molecular skeleton of important nucleobases (cytosine, uracil and thymine). Pyridine and pyrimidine are also expected to share similarities in their chemical behavior because of the presence of N in the aromatic ring in the place of one (pyridine) or two (pyrimidine) methine groups (=CH−).</p> <p>For the above reasons, in our laboratory we have undertaken a systematic experimental investigation to address pyridine stability in the conditions of primitive Earth. In a first series of experiments, we have exposed isolated pyridine molecules to the attack of very reactive species, namely atomic oxygen and nitrogen. The aim is to verify whether the N-containing aromatic ring of pyridine is preserved after the chemical attack of reactive transient species like O and N atoms that might have been relatively abundant under the conditions of primitive Earth when the O<sub>2</sub>/O<sub>3</sub> UV shield was not present yet. The employed experimental technique is the one described in Ref. [6]. The implications for the stability of pyridine and its derivatives, or of other molecules for which pyridine can be considered as a proxy, will be noted.</p> <p>The Authors wish to thank the Italian Space Agency for co-funding the <span class="markrnqlbh7dn" data-markjs="true" data-ogac="" data-ogab="" data-ogsc="" data-ogsb="">Life</span> in Space project (<span class="markn33axkulf" data-markjs="true" data-ogac="" data-ogab="" data-ogsc="" data-ogsb="">ASI</span> N. 2019-3-U.0).</p> <p> </p> <p>[1] P. G.Stoks, A. W. Schwartz. Basic nitrogen-heterocyclic compounds in the Murchison meteorite. Geochimica et Cosmochimica Acta 46, 309-315 (1982).</p> <p>[2] Y. Yamashita, H. Naraoka. Two homologous series of alkylpyridines in the Murchison meteorite. Geochemical Journal 48, 519-525, (2014).</p> <p>[3] S. Pizzarello, Y. Huang, L. Becker, R. J. Poreda, R. A. Nieman, G. Cooper, M. Williams. The Organic Content of the Tagish Lake Meteorite. Science 293, 2236- 2239 (2001).</p> <p>[4] K. E. Smith, M. P. Callahan, P. A. Gerakines, J. P. Dworkin, C. H. House. Investigation of pyridine carboxylic acids in CM2 carbonaceous chondrites: Potential precursor molecules for ancient coenzymes. Geochimica et Cosmochimica Acta 136, 1–12 (2014).</p> <p>[5] N. Friedmann, S. L. Miller, R. A. Sanchez. Primitive Earth Synthesis of Nicotinic Acid Derivatives. Science Vol. 171, 1026-1027 (1971).</p> <p>[6] N. Balucani. Elementary reactions of N atoms with hydrocarbons: first steps towards the formation of prebiotic N-containing molecules in planetary atmospheres. Chem. Soc. Rev. 41, 5473–5483 (2012).</p>

Evidence for Proteogenic Peptide-like Sequences in Meteorites Through an Enzyme-Catalysed Stereoselective Hydrolysis Strategy

In this manuscript, we evidenced for the first time proteogenic like peptide sequences in meteorite thanks to an original stereoselective enzymatic hydrolysis. Within this framework, we have first characterised the amino acids content of two meteorites, Murchison and Allende, after the standard acid hydrolysis protocol currently used in astronomical studies. To reach this goal, we have developed a highly sensitive chiral LC-MS method and we have highlighted new l- and d-enantiomers, never detected before in both meteorites. These primary findings extend the list of amino acids already found in meteorites. We next investigated the presence of proteogenic like peptide sequences. For that, we have compared the amounts of amino acids l- and d-enantiomers released from either the standard acid hydrolysis or our stereoselective peptidase hydrolysis. Thanks to this strategy, we have highlighted the presence of peptide sequences involving proteogenic l-amino acids in the Murchison together with their absence in Allende, which is consistent with the respective organic content of both meteorites. Furthermore, we demonstrated that the peptide sequences were indigenous to the Murchison meteorite.<br>

Evidence for Proteogenic Peptide-like Sequences in Meteorites Through an Enzyme-Catalysed Stereoselective Hydrolysis Strategy

In this manuscript, we evidenced for the first time proteogenic like peptide sequences in meteorite thanks to an original stereoselective enzymatic hydrolysis. Within this framework, we have first characterised the amino acids content of two meteorites, Murchison and Allende, after the standard acid hydrolysis protocol currently used in astronomical studies. To reach this goal, we have developed a highly sensitive chiral LC-MS method and we have highlighted new l- and d-enantiomers, never detected before in both meteorites. These primary findings extend the list of amino acids already found in meteorites. We next investigated the presence of proteogenic like peptide sequences. For that, we have compared the amounts of amino acids l- and d-enantiomers released from either the standard acid hydrolysis or our stereoselective peptidase hydrolysis. Thanks to this strategy, we have highlighted the presence of peptide sequences involving proteogenic l-amino acids in the Murchison together with their absence in Allende, which is consistent with the respective organic content of both meteorites. Furthermore, we demonstrated that the peptide sequences were indigenous to the Murchison meteorite.<br>

Origin of alkylphosphonic acids in the interstellar medium

For decades, the source of phosphorus incorporated into Earth’s first organisms has remained a fundamental, unsolved puzzle. Although contemporary biomolecules incorporate P(+V) in their phosphate moieties, the limited bioavailability of phosphates led to the proposal that more soluble P(+III) compounds served as the initial source of phosphorus. Here, we report via laboratory simulation experiments that the three simplest alkylphosphonic acids, soluble organic phosphorus P(+III) compounds, can be efficiently generated in interstellar, phosphine-doped ices through interaction with galactic cosmic rays. This discovery opens a previously overlooked avenue into the formation of key molecules of astrobiological significance and untangles basic mechanisms of a facile synthesis of phosphorus-containing organics in extraterrestrial ices, which can be incorporated into comets and asteroids before their delivery and detection on Earth such as in the Murchison meteorite.