César Menor-Salván

Synthesis of Pyrimidines and Triazines in Ice: Implications for the Prebiotic Chemistry of Nucleobases

Herein, we report the efficient synthesis of RNA bases and functionalized s-triazines from 0.1 M urea solutions in water after subjection to freeze-thaw cycles for three weeks. The icy solution was under a reductive, methane-based atmosphere, which was subjected to spark discharges as an energy source for the first 72 h of the experiment. Analysis of the products indicates the synthesis of the s-triazines cyanuric acid, ammeline, ammelide, and melamine, the pyrimidines cytosine, uracil, and 2,4-diaminopyrimidine, and the purine adenine. An experiment performed as a control at room temperature, with the urea solution in the liquid phase and with the same atmosphere and energy source, led to the synthesis of hydantoins and insoluble tholin, but there was no evidence of the synthesis of pyrimidines or triazines. The synthesis of pyrimidines from urea is possible under a methane/nitrogen atmosphere only at low temperature, in the solid phase. The generation of both pyrimidines and triazines in comparable yields from urea, together with a possible role for triazines as alternative nucleobases, opens new perspectives on the prebiotic chemistry of informational polymers.

Prebiotic microreactors: A synthesis of purines and dihydroxy compounds in aqueous aerosol

We report the synthesis of purine bases and other heterocycles and the formation of amino acids, hydroxy acids and dihydroxy compounds by the spark activation of an atmosphere of methane, nitrogen and hydrogen, in the presence of an aqueous aerosol. With the aid of the interface air–water, the organic material obtained shows greater amounts and diversity of molecules with biological interest than the products obtained in the absence of an aerosol. Our results support the suggestion that aerosols may have played a significant role in the prebiotic origin of molecular diversity and evolution.

Classification of Modern and Old Río Tinto Sedimentary Deposits Through the Biomolecular Record Using a Life Marker Biochip: Implications for Detecting Life on Mars

The particular mineralogy formed in the acidic conditions of the Río Tinto has proven to be a first-order analogue for the acid-sulfate aqueous environments of Mars. Therefore, studies about the formation and preservation of biosignatures in the Río Tinto will provide insights into equivalent processes on Mars. We characterized the biomolecular patterns recorded in samples of modern and old fluvial sediments along a segment of the river by means of an antibody microarray containing more than 200 antibodies (LDCHIP200, for Life Detector Chip) against whole microorganisms, universal biomolecules, or environmental extracts. Samples containing 0.3-0.5 g of solid material were automatically analyzed in situ by the Signs Of LIfe Detector instrument (SOLID2), and the results were corroborated by extensive analysis in the laboratory. Positive antigen-antibody reactions indicated the presence of microbial strains or high-molecular-weight biopolymers that originated from them. The LDCHIP200 results were quantified and subjected to a multivariate analysis for immunoprofiling. We associated similar immunopatterns, and biomolecular markers, to samples with similar sedimentary age. Phyllosilicate-rich samples from modern fluvial sediments gave strong positive reactions with antibodies against bacteria of the genus Acidithiobacillus and against biochemical extracts from Río Tinto sediments and biofilms. These samples contained high amounts of sugars (mostly polysaccharides) with monosaccharides like glucose, rhamnose, fucose, and so on. By contrast, the older deposits, which are a mix of clastic sands and evaporites, showed only a few positives with LDCHIP200, consistent with lower protein and sugar content. We conclude that LDCHIP200 results can establish a correlation between microenvironments, diagenetic stages, and age with the biomarker profile associated with a sample. Our results would help in the search for putative martian biomarkers in acidic deposits with similar diagenetic maturity. Our LDCHIP200 and SOLID-like instruments may be excellent tools for the search for molecular biomarkers on Mars or other planets.

New insights into the characterization of 'insoluble black HCN polymers'.

The data presented here provide a novel contribution to the understanding of the structural features of HCN polymers and could be useful in further development of models for prebiotic chemistry. The interpretation of spectroscopic and analytical data, along with previous results reported by other authors, allowed us to propose a mechanism for the aqueous polymerization of HCN from its primary and simplest isolated oligomer, the diaminomaleonitrile (DAMN) tetramer. We suggest that ‘insoluble black HCN polymers’ are formed by an unsaturated complex matrix, which retains a significant amount of H2O and important bioorganic compounds or their precursors. This polymeric matrix can be formed by various motifs of imidazoles and cyclic amides, among others. The robust formation of HCN polymers assayed under several conditions seems to explain the plausible ubiquity of these complex substances in space.

Thermal Wet Decomposition of Prussian Blue: Implications for Prebiotic Chemistry

The complex salt named Prussian Blue, Fe4[Fe(CN)6]3⋅15 H2O, can release cyanide at pH>10. From the point of view of the origin of life, this fact is of interest, since the oligomers of HCN, formed in the presence of ammonium or amines, leads to a variety of biomolecules. In this work, for the first time, the thermal wet decomposition of Prussian Blue was studied. To establish the influence of temperature and reaction time on the ability of Prussian Blue to release cyanide and to subsequently generate other compounds, suspensions of Prussian Blue were heated at temperatures from room temperature to 150° at pH 12 in NH3 environment for several days. The NH3 wet decomposition of Prussian Blue generated hematite, α‐Fe2O3, the soluble complex salt (NH4)4[Fe(CN6)]⋅1.5 H2O, and several organic compounds, the nature and yield of which depend on the experimental conditions. Urea, lactic acid, 5,5‐dimethylhydantoin, and several amino acids and carboxylic acids were identified by their trimethylsilyl (TMS) derivatives. HCN, cyanogen (C2N2), and formamide (HCONH2) were detected in the gas phase by GC/MS analysis.

Synthesis of Polycyclic Aromatic Hydrocarbons and Acetylene Polymers in Ice: A Prebiotic Scenario

The recent evidences of presence of subsurface oceans of liquid water and ice on Saturns moons, and the possible presence and astrobiological importance of polycyclic aromatic hydrocarbons (PAHs) in these environments, provide strong motivation for the exploration of the prebiotic chemistry in ice and to test if PAHs could be experimentally synthesized in ice surfaces under atmospheres containing methane as carbon source. In this work, we present a new design for prebiotic‐chemistry experiments in ice matrix. Using this design, a mixture of products including PAHs, polar aromatic compounds, and hydrophilic acetylene‐based polymers was obtained. We propose that acetylene generation in a methane/nitrogen atmosphere and subsequent polymerization to PAHs and polyynes could be a favored pathway in the presence of water freeze–melt cycles. These results shed light on the processes involved in PAH synthesis in icy environments and on the physical factors that drive the different competing pathways in methane/nitrogen atmospheres.