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A Search for Amino Acids and Nucleobases in the Martian Meteorite Roberts Massif 04262 Using Liquid Chromatography-Mass Spectrometry

The investigation into whether Mars contains signatures of past or present life is of great interest to science and society. Amino acids and nucleobases are compounds that are essential for all known life on Earth and are excellent target molecules in the search for potential Martian biomarkers or prebiotic chemistry. Martian meteorites represent the only samples from Mars that can be studied directly in the laboratory on Earth. Here, we analyzed the amino acid and nucleobase content of the shergottite Roberts Massif (RBT) 04262 using liquid chromatography-mass spectrometry. We did not detect any nucleobases above our detection limit in formic acid extracts; however, we did measure a suite of protein and nonprotein amino acids in hot-water extracts with high relative abundances of beta-alanine and gamma-amino-eta-butyric acid. The presence of only low (to absent) levels of several proteinogenic amino acids and a lack of nucleobases suggest that this meteorite fragment is fairly uncontaminated with respect to these common biological compounds. The distribution of straight-chained amine-terminal eta-omega-amino acids in RBT 04262 resembled those previously measured in thermally altered carbonaceous meteorites. A carbon isotope ratio of -24(0/00) +/- 6(0/00) for beta-alanine in RBT 04262 is in the range of reduced organic carbon previously measured in Martian meteorites (Steele et al. 2012). The presence of eta-omega-amino acids may be due to a high temperature Fischer-Tropschtype synthesis during igneous processing on Mars or impact ejection of the meteorites from Mars, but more experimental data are needed to support these hypotheses.

Laboratory analysis↗

Liquid Chromatography-Mass Spectrometry Interface for Detection of Extraterrestrial Organics

The OASIS (Organics Analyzer for Sampling Icy surfaces) microchip enables electrospray or thermospray of analyte for subsequent analysis by the OASIS time-of-flight mass spectrometer. Electrospray of buffer solution containing the nucleobase adenine was performed using the microchip and detected by a commercial time-of-flight mass spectrometer. Future testing of thermospray and electrospray capability will be performed using a test fixture and vacuum chamber developed especially for optimization of ion spray at atmosphere and in low pressure environments.

extraterrestrial organics↗

INCORPORATION OF NITROGEN INTO ORGANICS PRODUCED BY FISCHER-TROPSCH TYPE CHEMISTRY

Laboratory simulations have demonstrated that hydrothermal systems have the potential to produce a range of organic compounds through Fischer-Tropsch type (FTT) chemistry. The distribution of products depends on several factors, including the abundance and composition of feedstock molecules, reaction temperature, and the physical and chemical characteristics of catalytic materials included in the reactions. The majority of studies per-formed to date have focused solely on inclusion of CO2 or CO and H2 as the carbon, oxygen and hydrogen sources, which limits the possible products to hydrocarbons, alcohols and carboxylic acids. A few studies have included nitrogen in the form of ammonia, which led to the production of amino acids and nitrogenous bases. Although these demonstrations provide compelling evidence that FTT reactions can produce compounds of interest for the origins of life, such reactions have been conducted under a very limited range of conditions and the synthetic reaction mechanisms have generally not been well-characterized. We have begun a series of laboratory experiments that will incorporate a range of precursor molecules in varying compositions to determine how these variables affect the relative amounts and speciation of life-essential elements in organic molecules produced under FTT conditions. In the present work, we focus on systems containing C, H, O and N. Reaction mixtures contained CO (~60-80 mM), 150 mM ammonium chloride, and water with a native iron catalyst, which also served as a source of H2 through the reduction of water. Three initial experiments were conducted at 110, 154 and 185 °C and heated for several days. Following the reaction, samples were analyzed by gas chromatography-mass spectrometry, direct analysis in real time mass spectrometry and liquid chromatography-mass spectrometry.

A. S. Burton↗

Xeropreservation of Functionalized Lipid Biomarkers in Hyperarid Soils in the Atacama Desert

Our understanding of long-term organic matter preservation comes mostly from studies in aquatic systems. In contrast, taphonomic processes in extremely dry environments are relatively understudied and are poorly understood. We investigated the accumulation and preservation of lipid biomarkers in hyperarid soils in the Yungay region of the Atacama Desert. Lipids from seven soil horizons in a 2.5 meter vertical profile were extracted and analyzed using GC-MS ( Gas Chromatography-Mass Spectrometry) and LC-MS (Liquid Chromatography-Mass Spectrometry). Diagnostic functionalized lipids and geolipids were detected and increased in abundance and diversity with depth. Deeper clay units contain fossil organic matter (radiocarbon dead) that has been protected from rainwater since the onset of hyperaridity. We show that these clay units contain lipids in an excellent state of structural preservation with functional groups and unsaturated bonds in carbon chains. This indicates that minimal degradation of lipids has occurred in these soils since the time of their deposition between more than 40,000 and up to 2 million years ago. The exceptional structural preservation of biomarkers is likely due to the long-term hyperaridity that has minimized microbial and enzymatic activity, a taphonomic process we term xeropreservation (i.e. preservation by drying). The degree of biomarker preservation allowed us to reconstruct major changes in ecology in the Yungay region that reflect a shift in hydrological regime from wet to dry since the early Quaternary. Our results suggest that hyperarid environments, which comprise 7.5 percent of the continental landmass, could represent a rich and relatively unexplored source of paleobiological information on Earth.

Xeropreservation↗

Analysis of Chiral Carboxylic Acids in Meteorites

Homochirality of amino acids in proteins and sugars in DNA and RNA is a critical feature of life on Earth. In the absence of a chiral driving force, however, reactions leading to the synthesis of amino acids and sugars result in racemic mixtures. It is currently unknown whether homochirality was necessary for the origins of life or if it was a product of early life. The observation of enantiomeric excesses of certain amino acids of extraterrestrial origins in meteorites provides evidence to support the hypothesis that there was a mechanism for the preferential synthesis or destruction of a particular amino acid enantiomer [e.g., 1-3]. The cause of the observed chiral excesses is un-clear, although at least in the case of the amino acid isovaline, the degree of aqueous alteration that occurred on the meteorite parent body is correlated to the isovaline L-enantiomeric excess [3, 4]. This suggests that chiral symmetry is broken and/or amplified within the meteorite parent bodies. Besides amino acids, there have been only a few reports of other meteoritic compounds found in enantiomeric excess: sugars and sugar acids [5, 6] and the hydroxy acid lactic acid [7]. Determining whether or not additional types of molecules in meteorites are also present in enantiomeric excesses of extraterrestrial information will provide insights into mechanisms for breaking chiral symmetry. Though the previous measurements (e.g., enantiomeric composition of lactic acid [7], and chiral carboxylic acids [8]) were made by gas chromatography-mass spectrometry, the potential for increased sensitivity of liquid chromatography-mass spectrometry (LC-MS) analyses is important because for many meteorite samples, only small sample masses are available for study. Furthermore, at least in the case of amino acids, many of the largest amino acid enantiomeric excesses were observed in samples that contained lower abundances (tens of ppb) of a given amino acid enantiomer. In the present work, we describe our efforts to develop highly sensitive LC-MS methods for the analysis of chiral carboxylic acids including hydroxy acids.

Burton, A. S.↗

Prebiotic synthesis of histidine

The prebiotic formation of histidine (His) has been accomplished experimentally by the reaction of erythrose with formamidine followed by a Strecker synthesis. In the first step of this reaction sequence, the formation of imidazole-4-acetaldehyde took place by the condensation of erythrose and formamidine, two compounds that are known to be formed under prebiotic conditions. In a second step, the imidazole-4-acetaldehyde was converted to His, without isolation of the reaction products by adding HCN and ammonia to the reaction mixture. LC, HPLC, thermospray liquid chromatography-mass spectrometry, and tandem mass spectrometry were used to identify the product, which was obtained in a yield of 3.5% based on the ratio of His/erythrose. This is a new chemical synthesis of one of the basic amino acids which had not been synthesized prebiotically until now.

Non-NASA Center↗

Carbonaceous Meteorites Contain a Wide Range of Extraterrestrial Nucleobases

All terrestrial organisms depend on nucleic acids (RNA and DNA), which use pyrimidine and purine nucleobases to encode genetic information. Carbon-rich meteorites may have been important sources of organic compounds required for the emergence of life on the early Earth; however, the origin and formation of nuc1eobases in meteorites has been debated for over 50 y. So far, the few nuc1eobases reported in meteorites are biologically common and lacked the structural diversity typical of other indigenous meteoritic organics. Here, we investigated the abundance and distribution of nucleobases and nucleobase analogs in formic acid extracts of 12 different meteorites by liquid chromatography-mass spectrometry. The Murchison and Lonewolf Nunataks 94102 meteorites contained a diverse suite of nucleobases, which included three unusual and terrestrially rare nucleobase analogs; purine, 2,6-diminopurine, and 6,8-diaminopurine. In a parallel experiment, we found an identical suite of nucleobases and nucleobase analogs generated in reactions of ammonium cyanide. Additionally, these nucleobase analoge were not detected above our parts-per-billion detection limits in any of the procedural blanks, control samples, a terrestrial soil sample, and an Antarctic ice sample. Our results demonstrate that the purines detected in meteorites are consistent with products of ammonium cyanide chemistry, which provides a plausible mechanism for their synthesis in the asteroid parent bodies, and strongly supports an extraterrestrial origin. The discovery of new nucleobase analogs in meteorites also expands the prebiotic molecular inventory available for constructing the first genetic molecules.

Callahan, Michael P.↗

Experimental Studies on the Effect of Impact Processes on the Formation and Evolution of Amino Acids

Introduction: A critical step in the emergence of life on Earth was the synthesis of larger organic molecules from simple building blocks such as NH3, CO2, H2O, and CH3OH. The presence of amino acids and other complex organics in comets and meteorites demonstrates that widespread organic synthesis likely occurred across the early solar system. Building on previous work [e.g., 1-3], we systematically explore impact-driven chemical evolution of exogenous organics and their precursors. Collisional processes may also have provided a source of energy for the formation of more complex organics from endogenous building blocks. The high flux of impactors to Earth immediately prior to and during the origins of life suggests that impacts could have played a critical role. Key Questions: 1. How are the formation and evolution of amino acids affected by the presence of a mineral matrix during cometary and asteroidal impacts onto the early Earth? 2. Do some minerals (e.g., phyllosilicates) provide a more robust protective framework or reactive surface site for amino-acid formation and/or polymerization? 3. Does the abundance of ices and/or amino acids relative to that of the mineral matrix affect the formation and evolution of amino acids? 4. Are there impact velocities/shock pressures at which formation or polymerization of amino acids is favored or precluded? Experimental Approach: This study systematically examines the conditions under which amino acids and other organic molecules can form, be polymerized, and/or be destroyed during impact events into particulate regolith simulants. Variable parameters include the modal composition of this regolith (silicate matrices, ratios of ices, silicates, and amino acids) and impact velocities/shock pressures. Impacts experiments were performed using the two-stage light-gas gun (LGG), vertical gun (VG), and flat-plate accelerator (FPA) in the Experimental Impact Lab at JSC. FPA experiments were performed over a range of shock pressures (11.3-31.5 GPa) using CM chondrite simulant mixed with amino acids at ratios of 0:10, 1:10, 1:103, and 1:106 (amino acid:host). Techniques for mixing cometary ices have been optimized and test runs have been performed using the LGG (see figure below). Analysis: Post-impact, samples are heated in water to extract amino acids and peptides. Extracts are characterized via liquid chromatography-mass spectrometry (LC-MS) and the mineralogies of solid residues are characterized using X-ray diffraction, scanning electron microscopy and transmission electron microscopy. Additional LC-MS and mineralogical analyses are underway.

Eve L Berger↗

Extraterrestrial Amino Acids and Amines Identified in Asteroid Ryugu Samples Returned By the Hayabusa2 Mission

The hot water and acid extracts of two different Ryugu samples collected by the Hayabusa2 mission were analyzed for the presence of aliphatic amines and amino acids. The abundances and relative distributions of both classes of molecules were determined, as well as the enantiomeric compositions of the chiral amino acids. The Ryugu samples studied here were recovered from sample chambers A and C, which were composed of surface material, and a combination of surface and possible subsurface material, respectively. A total of thirteen amino acids were detected and quantitated in these samples, with an additional five amino acids that were tentatively identified but not quantitated. The abundances of four aliphatic amines identified in the Ryugu samples were also determined in the current work. Amino acids were observed in the acid hydrolyzed and unhydrolyzed hot water extracts of asteroid Ryugu regolith using liquid chromatography with UV fluorescence detection and high-resolution mass spectrometry. Conversely, aliphatic amines were only analyzed in the unhydrolyzed hot water Ryugu extracts. Two- to six-carbon (C 2 -C 6 ) amino acids with individual abundances ranging from 0.02 to 15.8 nmol g −1 , and one- to three-carbon (C 1 -C 3 ) aliphatic amines with individual abundances from 0.05 to 34.14 nmol g −1 , were found in the hot water extracts. Several non-protein amino acids that are rare in biology, including β-amino-n-butyric acid (β-ABA) and β-aminoisobuytric acid (β-AIB), were racemic or very nearly racemic, thus indicating their likely abiotic origins. Trace amounts of select protein amino acids that were enriched in the ւ-enantiomer may indicate low levels of terrestrial amino acid contamination in the samples. However, the presence of elevated abundances of free and racemic alanine, a common protein amino acid in terrestrial biology, and elevated abundances of the predominately free and racemic non-protein amino acids, β-ABA and β-AIB, indicate that many of the amino acids detected in the Ryugu water extracts were indigenous to the samples. Although the Ryugu samples have been found to be chemically similar to CI type carbonaceous chondrites, the measured concentrations and relative distributions of amino acids and aliphatic amines in Ryugu samples were notably different from those previously observed for the CI1.1 carbonaceous chondrite, Orgueil. This discrepancy could be the result of differences in the original chemical compositions of the parent bodies and/or alteration conditions, such as space weathering. In addition to α-amino acids that could have been formed by Strecker cyanohydrin synthesis during a low temperature aqueous alteration phase, β-, γ-, and δ-amino acids, including C 3 – C 5 straight-chain n-ω-amino acids that are not formed by Strecker synthesis, were also observed in the Ryugu extracts. The suite of amino acids measured in the Ryugu samples indicates that multiple amino acid formation mechanisms were active on the Ryugu parent body. The analytical techniques used here are well-suited to search for similar analytes in asteroid Bennu material collected by the NASA OSIRIS-REx mission scheduled for Earth return in September 2023.

Hayabusa2↗

Investigation of Isovaline Enantiomeric Excesses and Other C5 Amino Acids in Carbonaceous Meteorites

The origin of biological homochirality is one of the most perplexing puzzles to understanding the emergence of life on Earth. While many models have been proposed, the only reported non-biologically generated. compounds that show a significant enantiomeric excess are a few amino acids in the CM2 Murchison and Murray meteorites (e.g. Pizzarello and Cronin 2000; Pizzarello et al, 2008). Of these isovaline (alpha-ethyl-alanine) is of particular interest since it is typically abundant in CM2 meteorites, is exceedingly rare in biology, and due to its chemical structure is likely to maintain its primordial D/L ratio. Instead of the gas chromatography-mass spectrometry (GC-MS) technique employed by Pizzarello et al., we have used liquid chromatography-fluorescence detection/time of flight-mass spectrometry (LC-FD/ToF-MS) to study the enantiomeric ratio of isovaline in the CM2 meteorites Murchison and LEW90500 and the CR2 QUE99177. We have placed particular emphasis on understanding the suite of C5 amino acids in these meteorites. In doing so, we have determined that D and L 3-aminopentanoic acid co-elutes with Lisovaline and L-valine under common chromatographic conditions (Glavin and Dworkin 2006) for omicron-phthaldialdehyde/N-acetyl-L-cysteine (OPA/NAC). We have devised a method to separate these compounds and we will report the actual D/ L ratios of isovaline in these meteorites and how they compare to the GC-MS measurements of Pizzarello and co-workers.

Dworkin, Jason P.↗