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Evaluating the distribution and diversity of solvent-soluble organic molecules in extraterrestrial materials provide information about the physicochemical environments where prebiotic chemistry occurred and is essential for assessing the inventory of prebiotic compounds available to the early Earth. In this work, we conducted a comprehensive molecular characterization of solvent-soluble organic compounds in a homogenized aggregate sample (ID: OREX-800107-128) of unsorted regolith from asteroid (101955) Bennu returned by NASA’s OSIRIS-REx mission. Using two-dimensional gas chromatography coupled with high-resolution time-of-flight mass spectrometry (GC×GC-HRMS), we identified 87 organic compounds across several molecular classes, including alkanes, polycyclic aromatic hydrocarbons, and nitrogen-, oxygen-, and sulfur-bearing species. Comparison with the organic inventory of CI (Orgueil), C2-ungrouped (Tagish Lake and Tarda), and CM2 (Murchison) carbonaceous chondrites revealed that Bennu sample OREX-800107-128 is most similar to Tagish Lake and Tarda yet compositionally distinct from all of these meteorites. This Bennu sample exhibits a relatively high abundance of low-molecular-weight aromatics (e.g., toluene), pyridine derivatives, and sulfur species such as dimethyl sulfite, consistent with episodic low-temperature aqueous alteration. The presence of these organic compounds suggests that this material experienced chemically diverse processes in the parent body conducive to complex organic synthesis, including aldol condensation reactions responsible for N- and O-bearing compounds. We also compared the molecular distributions of this Bennu sample and previously analyzed samples from (162173) Ryugu to assess potential common origins between these two carbonaceous asteroids. Bennu shows more chemically diverse and nitrogen-rich organic materials than Ryugu. While both asteroids share broadly similar primitive compositions, the observed chemical differences indicate distinct evolutionary histories within a likely common formation environment though whether Bennu and Ryugu derive from a single compositionally heterogeneous parent body or from multiple closely related progenitors remains unresolved. Further detailed comparative analyses of material from Bennu, Ryugu, and specific carbonaceous meteorites (e.g., Tagish Lake and Tarda) will provide new insights into how the N-rich molecular profile observed in Bennu samples was formed and evolved in the outer Solar System.
The organic compounds of carbonaceous chondrites are structurally diverse products of the prolonged abiotic chemistry that occurred before and during the early stages of the solar system. They also represent the types of prebiotic compounds that may have participated in chemical evolutionary processes that gave rise to life. Pyruvic acid is a key component of primary metabolism that has recently been found in carbonaceous chondrites. Its prominence in biology has inspired us to explore its chemistry and possible role in the origin of metabolism. Our laboratory investigations have found that pyruvate (the ionized form of pyruvic acid) can serve as a single-source reactant to generate what we term a pyruvate reaction network (PRN). The core of the PRN is driven by pyruvate aldol polymerization and decay reactions. These decay reactions lead to the production of stable and unstable compounds which include mono, di, and tricarboxylic acids and a variety of keto acids. Importantly, many of these reactions apparently lead back to pyruvate, establishing a feedback process. Finding evidence of this reaction network in meteorites would establish that the chemistry of pyruvate did occur in a prebiotic environment and indeed many of the known compounds found in pyruvate reaction mixtures were detected in the Murchison and Murray meteorites. However, multiple synthetic origins, not tied to pyruvate chemistry, might also explain their meteoritic presence. Thus finding compounds unique to the PRN, such as reaction intermediates, would provide stronger evidence in support of its prebiotic relevance. The identity of these intermediates can only be con-firmed by acquiring chemical standards, however, as most are not available commercially, we engaged in extensive chemical synthesis. Obtaining these standards also provides the opportunity to study their subsequent chemistry and roles in the PRN.
The organic compounds of carbonaceous chondrites are structurally diverse products of the prolonged abiotic chemistry that occurred before and during the early stages of the solar system. They also represent the types of prebiotic compounds that may have participated in chemical evolutionary processes that gave rise to life. Pyruvic acid is a key component of primary metabolism that has recently been found in carbonaceous chondrites. Its prominence in biology has inspired us to explore its chemistry and possible role in the origin of metabolism. Our laboratory investigations have found that pyruvate (the ionized form of pyruvic acid) can serve as a single-source reactant to generate what we term a pyruvate reaction network (PRN). The core of the PRN is driven by pyruvate aldol polymerization and decay reactions. These decay reactions lead to the production of stable and unstable compounds which include mono, di, and tricarboxylic acids and a variety of keto acids. Importantly, many of these reactions apparently lead back to pyruvate, establishing a feedback process. Finding evidence of this reaction network in meteorites would establish that the chemistry of pyruvate did occur in a prebiotic environment and indeed many of the known compounds found in pyruvate reaction mixtures were detected in the Murchison and Murray meteorites. However, multiple synthetic origins, not tied to pyruvate chemistry, might also explain their meteoritic presence. Thus finding compounds unique to the PRN, such as reaction intermediates, would provide stronger evidence in support of its prebiotic relevance. The identity of these intermediates can only be confirmed by acquiring chemical standards, however, as most are not available commercially, we engaged in extensive chemical synthesis. Obtaining these standards also provides the opportunity to study their subsequent chemistry and roles in the PRN.
The organic compounds of carbo- naceous chondrites are structurally diverse products of the prolonged abiotic chemistry that occurred before and during the early stages of the solar system [1]. They also represent the types of prebiotic compounds that may have participated in chemical evolutionary processes that gave rise to life [2]. Pyruvic acid is a key component of primary metabolism that has recently been found in carbonaceous chondrites [3]. Its prominence in biology has inspired us to explore its chemistry and possible role in the origin of metabolism. Our laboratory investigations have found that pyruvate (the ionized form of pyruvic acid) can serve as a single-source reactant to generate what we term a pyruvate reaction network (PRN). The core of the PRN is driven by pyruvate aldol polymerization and decay reactions. These decay reactions lead to the production of stable and unstable compounds which include mono, di, and tricarboxylic acids and a variety of keto acids. Finding evidence of this reaction network in meteorites would establish that the chemistry of pyruvate did occur in a prebiotic environment. Many of the known compounds found in pyruvate reaction mixtures were originally detected in meteorite samples by Cooper et al in 2011. However, multiple synthetic origins not tied to pyruvate chemistry might also explain their meteoritic presence. Thus, a search to find compounds unique to the PRN, such as reaction intermediates, would provide stronger evidence to demonstrate its prebiotic relevance. The identity of these intermediates can only be confirmed by acquiring chemical standards, however, as most are not available commercially, they need to be accessed through chemical synthesis.
Synthesis of sugars by Ca(OH)2 catalyzed formaldehyde condensation (the formose reaction) has produced branched carbohydrates that do not occur in nature. The kinetics and mechanisms of the homogeneously catalyzed autocatalytic condensation were studied and analogies between homogeneous and heterogeneous rate laws have been found. Aldol condensations proceed simultaneously with Cannizzaro and crossed-Cannizzaro reactions and Lobry de Bruyn-Van Eckenstein rearrangements. The separate steps as well as the interactions of this highly complex reaction system were elucidated. The system exhibits instabilities, competitive catalytic, mass action, and equilibrium phenomena, complexing, and parallel and consecutive reactions. Specific finding that have been made on the problem will be of interest for synthesizing sugars, both for sustained space flight and for large scale food manufacture. A contribution to methodology for studying complex catalyzed reactions and to understanding control of reaction selectivity was a broad goal of the project.
The origin of life can be described as a series of events in which a prebiotic chemical process came increasingly under the control of its catalytic products. In our search for this prebiotic process that yielded catalytic takeover products (such as polypeptides), we have been investigating a reaction system that generates peptide-forming amino acid thioesters from formaldehyde, glycolaldehyde, and ammonia in the presence of thiols. As shown below, this model process begins by aldol condensation of formaldehyde and glycolaldehyde to give trioses and releases. These sugars then undergo beta-dehydration yielding their respective alpha-ketoaldehydes. Addition of ammonia to the alpha-ketoaldehydes yields imines which can either: (a) rearrange in the presence of thesis to give amino acid thioesters or (be react with another molecule of aldehyde to give imidazoles. This 'one-pot' reaction system operates under mild aqueous conditions, and like modem amino acid biosynthesis, uses sugar intermediates which are converted to products by energy-yielding redox reactions. Recently, we discovered that amino acids, such as the alanine reaction product, catalyze the first and second steps of the process. In the presence of ammonia the process also generates other synthetically useful products, like the important biochemical -- pyruvic acid.
Environmental conditions play an important role in conceptual studies of prebiotically relevant chemical reactions that could have led to functional biomolecules. The necessary source compounds are likely to have been present in dilute solution, raising the question of how to achieve selective concentration and to reach activation. With the assumption of an initial 'RNA World', the questions of production, concentration, and interaction of aldehydes and aldehyde phosphates, potential precursors of sugar phosphates, come into the foreground. As a possible concentration process for simple, uncharged aldehydes, we investigated their adduct formation with sulfite ion bound in the interlayer of positively charged expanding-sheet-structure double-layer hydroxide minerals. Minerals of this type, initially with chloride as interlayer counter anion, have previously been shown to induce concentration and subsequent aldolization of aldehyde phosphates to form tetrose, pentose, and hexose phosphates. The reversible uptake of the simple aldehydes formaldehyde, glycolaldehyde, and glyceraldehyde by adduct formation with the immobilized sulfite ions is characterized by equilibrium constants of K=1.5, 9, and 11, respectively. This translates into an observable uptake at concentrations exceeding 50 mM.