Abstract:Chemical evolution, from simple molecules to complex systems, is fundamental to modern origins of life research, and complex reaction networks are often supposed to have operated on the early Earth. Herein, a variety of compounds useful particularly for RNA synthesis − namely, cyanogen chloride, cyanamide, and nitrile precursors to simple sugars − are produced in short order by a chemical reaction network starting from hydrogen cyanide and driven by gamma radiolysis. The radiolytic yield of cyanamide was found… Show more
“…Methanimine, formaldehyde, acetaldehyde, and 2-iminoethanol are inferred by the observation of aminoacetonitrile, glycolonitrile, lactonitrile, and serinenitrile, respectively, while glycolaldehyde is inferred from the direct NMR detection of its gem-diol form. Cyanogen chloride was observed in previously reported(35) radiolysis experiments under similar high NaCl concentrations. For further details of the proposed mechanisms, see SI Appendix, Schemes.…”
supporting
confidence: 56%
“…Both sources of energy have been shown capable of generating solvated electrons (eaq ) in aqueous environments, and in the case of γ rays, ionization of water is what leads to eaq in addition to hydroxyl radical (•OH) and hydrogen atom (•H) production. The generation of eaq in the presence of excess HCN has been shown to lead to simple sugars (35)(36)(37). This reaction works by a Kiliani-Fischer homologation mechanism, whereby eaq effectively serves as the reducing agent.…”
Section: Radiolysis As a Driving Forcementioning
confidence: 99%
“…The production of cyanamide relies on the oxidizing power achieved through the radiolysis of briny water, in a mechanism that likely depends (35) on chlorine radical (Cl•) generation (for more details, see ref. 35 and SI Appendix, Schemes). High concentrations of NaCl favor cyanamide through a pathway that may involve cyanogen chloride as an intermediate, a compound which was also observed (Scheme 3).…”
Continuous reaction networks, which do not rely on purification or timely additions of reagents, serve as models for chemical evolution and have been demonstrated for compounds thought to have played important roles for the origins of life such as amino acids, hydroxy acids, and sugars. Step-by-step chemical protocols for ribonucleotide synthesis are known, but demonstrating their synthesis in the context of continuous reaction networks remains a major challenge. Herein, compounds proposed to be important for prebiotic RNA synthesis, including glycolaldehyde, cyanamide, 2-aminooxazole, and 2-aminoimidazole, are generated from a continuous reaction network, starting from an aqueous mixture of NaCl, NH4Cl, phosphate, and HCN as the only carbon source. No well-timed addition of any other reagents is required. The reaction network is driven by a combination of γ radiolysis and dry-down. γ Radiolysis results in a complex mixture of organics, including the glycolaldehyde-derived glyceronitrile and cyanamide. This mixture is then dried down, generating free glycolaldehyde that then reacts with cyanamide/NH3to furnish a combination of 2-aminooxazole and 2-aminoimidazole. This continuous reaction network models how precursors for generating RNA and other classes of compounds may arise spontaneously from a complex mixture that originates from simple reagents.
“…Methanimine, formaldehyde, acetaldehyde, and 2-iminoethanol are inferred by the observation of aminoacetonitrile, glycolonitrile, lactonitrile, and serinenitrile, respectively, while glycolaldehyde is inferred from the direct NMR detection of its gem-diol form. Cyanogen chloride was observed in previously reported(35) radiolysis experiments under similar high NaCl concentrations. For further details of the proposed mechanisms, see SI Appendix, Schemes.…”
supporting
confidence: 56%
“…Both sources of energy have been shown capable of generating solvated electrons (eaq ) in aqueous environments, and in the case of γ rays, ionization of water is what leads to eaq in addition to hydroxyl radical (•OH) and hydrogen atom (•H) production. The generation of eaq in the presence of excess HCN has been shown to lead to simple sugars (35)(36)(37). This reaction works by a Kiliani-Fischer homologation mechanism, whereby eaq effectively serves as the reducing agent.…”
Section: Radiolysis As a Driving Forcementioning
confidence: 99%
“…The production of cyanamide relies on the oxidizing power achieved through the radiolysis of briny water, in a mechanism that likely depends (35) on chlorine radical (Cl•) generation (for more details, see ref. 35 and SI Appendix, Schemes). High concentrations of NaCl favor cyanamide through a pathway that may involve cyanogen chloride as an intermediate, a compound which was also observed (Scheme 3).…”
Continuous reaction networks, which do not rely on purification or timely additions of reagents, serve as models for chemical evolution and have been demonstrated for compounds thought to have played important roles for the origins of life such as amino acids, hydroxy acids, and sugars. Step-by-step chemical protocols for ribonucleotide synthesis are known, but demonstrating their synthesis in the context of continuous reaction networks remains a major challenge. Herein, compounds proposed to be important for prebiotic RNA synthesis, including glycolaldehyde, cyanamide, 2-aminooxazole, and 2-aminoimidazole, are generated from a continuous reaction network, starting from an aqueous mixture of NaCl, NH4Cl, phosphate, and HCN as the only carbon source. No well-timed addition of any other reagents is required. The reaction network is driven by a combination of γ radiolysis and dry-down. γ Radiolysis results in a complex mixture of organics, including the glycolaldehyde-derived glyceronitrile and cyanamide. This mixture is then dried down, generating free glycolaldehyde that then reacts with cyanamide/NH3to furnish a combination of 2-aminooxazole and 2-aminoimidazole. This continuous reaction network models how precursors for generating RNA and other classes of compounds may arise spontaneously from a complex mixture that originates from simple reagents.
“…It was recently demonstrated that radiolysis, by means of a continuous reaction network, generates a complex mixture of products that includes precursors for nucleotide synthesis 48 . These findings add to a growing body of evidence that radicals provide particularly efficient means of connecting geochemical substrates to macromolecular precursors with minimal experimental intervention 2 , 12 , 49 – 54 . Here we analyse the structure of a reaction network compiled from hundreds of experiments conducted over 60 years of research that links common geochemical substrates (CO 2 , H 2 O, N 2 , NaCl, chlorapatite and pyrite) to radiolytically-produced prebiotic precursors, and compare this network to life and its ecologies 55 – 57 .…”
Section: Introductionmentioning
confidence: 53%
“…Amino acids are produced through a combination of radiolysis and acid-hydrolysis of uncharacterised polymers 2 , 61 . Nucleotide precursors that lead to cytidine and uridine cyclic phosphates are all present within the network 48 , 49 , 62 . Figure 1 Visualisation and statistical analysis of radiolysis network.…”
The architectural features of cellular life and its ecologies at larger scales are built upon foundational networks of reactions between molecules that avoid a collapse to equilibrium. The search for life’s origins is, in some respects, a search for biotic network attributes in abiotic chemical systems. Radiation chemistry has long been employed to model prebiotic reaction networks, and here we report network-level analyses carried out on a compiled database of radiolysis reactions, acquired by the scientific community over decades of research. The resulting network shows robust connections between abundant geochemical reservoirs and the production of carboxylic acids, amino acids, and ribonucleotide precursors—the chemistry of which is predominantly dependent on radicals. Moreover, the network exhibits the following measurable attributes associated with biological systems: (1) the species connectivity histogram exhibits a heterogeneous (heavy-tailed) distribution, (2) overlapping families of closed-loop cycles, and (3) a hierarchical arrangement of chemical species with a bottom-heavy energy-size spectrum. The latter attribute is implicated with stability and entropy production in complex systems, notably in ecology where it is known as a trophic pyramid. Radiolysis is implicated as a driver of abiotic chemical organization and could provide insights about the complex and perhaps radical-dependent mechanisms associated with life’s origins.
Die Evolution der Coenzyme oder ihr Einfluss auf den Ursprung des Lebens ist grundlegend für das Verständnis unserer eigenen Existenz. Hypothesen über die Entstehung präbiotischer chemischer Bausteine, die unter paläogeochemischen Bedingungen wahrscheinlich entstanden – hierzu zählen auch niedermolekulare Verbindungen wie die Coenzyme – führen zu komplexeren Makromolekülen wie RNA. Damit erhält die Frage der Herkunft von Coenzymen und ihrer Beziehung in der Evolution der funktionellen Biochemie neuen Auftrieb. Viele Coenzyme weisen eine einfache chemische Struktur auf und leiten sich von Nukleotiden ab, was darauf hindeutet, dass sie mit der Entstehung der RNA koexistiert und eine zentrale Rolle im frühen Metabolismus gespielt haben könnten. Auf der Grundlage aktueller Theorien der präbiotischen Evolution werden in diesem Aufsatz plausible Hypothesen über die präbiotische Bildung von Schlüsselelementen innerhalb ausgewählter Coenzyme diskutiert. In Kombination mit präbiotischer RNA haben Coenzyme möglicherweise die frühen protometabolischen Netzwerke und die katalytischen Möglichkeiten der RNA während der Evolution des Lebens deutlich erweitert.
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