A reassessment of prebiotic organic synthesis in neutral planetary atmospheres

CO2 Fixation to Prebiotic Intermediates over Heterogeneous Catalysts

ConspectusThe study of the origin of life requires a multifaceted approach to understanding where and how life arose on Earth. One of the most compelling hypotheses is the chemosynthetic origin of life at hydrothermal vents, as this condition has been considered viable for early forms of life. The continuous production of H2 and heat by serpentinization generates reductive conditions at hydrothermal vents, in which CO2 can be used to build large biomolecules. Although this involves surface catalysis and an autocatalytic process, in which solid minerals act as catalysts in the conversion of CO2 to metabolically important organic molecules, the systematic investigation of heterogeneous catalysis to comprehend prebiotic chemistry at hydrothermal vents has not been undertaken.In this Account, we discuss geochemical CO2 fixation to metabolic intermediates by synthetic minerals at hydrothermal vents from the perspective of heterogeneous catalysis. Ni and Fe are the most abundant transition metals at hydrothermal vents and occur in the active site of the enzymes carbon monoxide dehydrogenases/acetyl coenzyme A synthases (CODH/ACS). Synthetic free-standing NiFe alloy nanoparticles can convert CO2 to acetyl coenzyme A pathway intermediates such as formate, acetate, and pyruvate. The same alloy can further convert pyruvate to citramalate, which is essential in the biological citramalate pathway. Thermal treatment of Ni3Fe nanoparticles under NH3, which can occur in hydrothermal vents, results in Ni3FeN/Ni3Fe heterostructures. This catalyst has been demonstrated to produce prebiotic formamide and acetamide from CO2 and H2O using Ni3FeN/Ni3Fe as both substrate and catalyst. In the process of serpentinization, Co can be reduced in the vicinity of olivine, a Mg-Fe silicate mineral. This produces CoFe and CoFe2 with serpentine in nature, representing SiO2-supported CoFe alloys. In mimicking these natural minerals, synthetic SiO2-supported CoFe alloys demonstrate the same liquid products as NiFe alloys, namely, formate, acetate, and pyruvate under mild hydrothermal vent conditions. In contrast to the NiFe system, hydrocarbons up to C6 were detected in the gas phase, which is also present in hydrothermal vents. The addition of alkali and alkaline-earth metals to the catalysts results in enhanced formate concentration, playing a promotional role in CO2 reduction. Finally, Co was loaded onto ordered mesoporous SiO2 after modification with cations to simulate the minerals found in hydrothermal vents. These catalysts were then investigated under diminished H2O concentration, revealing the conversion of CO2 to CO, CH4, methanol, and acetate. Notably, the selectivity to metabolically relevant methanol was enhanced in the presence of cations that could generate and stabilize the methoxy intermediate. Calculation using the machine learning approach revealed the possibility of predicting the selectivity of CO2 fixation when modifying mesoporous SiO2 supports with heterocations. Our research demonstrates that minerals at hydrothermal vents can convert CO2 into metabolites under a variety of prebiotic conditions, potentially paving the way for modern biological CO2 fixation processes.

On the scientific credibility of paleoanthropology

Smith and Smith and Wood proposed that the human fossil record offers special challenges for causal hypotheses because "unique" adaptations resist the comparative method. We challenge their notions of "uniqueness" and offer a refutation of the idea that there is something epistemologically special about human prehistoric data. Although paleontological data may be sparse, there is nothing inherent about this information that prevents its use in the inductive or deductive process, nor in the generation and testing of scientific hypotheses. The imprecision of the fossil record is well-understood, and such imprecision is often factored into hypotheses and methods. While we acknowledge some oversteps within the discipline, we also note that the history of paleoanthropology is clearly one of progress, with ideas tested and resolution added as data (fossils) are uncovered and new technologies applied, much like in sciences as diverse as astronomy, molecular genetics, and geology.

From Zero to Hero: The Cyanide-Free Formation of Amino Acids and Amides from Acetylene, Ammonia and Carbon Monoxide in Aqueous Environments in a Simulated Hadean Scenario

Amino acids are one of the most important building blocks of life. During the biochemical process of translation, cells sequentially connect amino acids via amide bonds to synthesize proteins, using the genetic information in messenger RNA (mRNA) as a template. From a prebiotic perspective (i.e., without enzymatic catalysis), joining amino acids to peptides via amide bonds is difficult due to the highly endergonic nature of the condensation reaction. We show here that amides can be formed in reactions catalyzed by the transition metal sulfides from acetylene, carbon monoxide and ammonia under aqueous conditions. Some α- and β-amino acids were also formed under the same conditions, demonstrating an alternative cyanide-free path for the formation of amino acids in prebiotic environments. Experiments performed with stable isotope labeled precursors, like 15NH4Cl and 13C-acetylene, enabled the accurate mass spectroscopic identification of the products formed from the starting materials and their composition. Reactions catalyzed using the transition metal sulfides seem to offer a promising alternative pathway for the formation of amides and amino acids in prebiotic environments, bypassing the challenges posed by the highly endergonic condensation reaction. These findings shed light on the potential mechanisms by which the building blocks of life could have originated on early Earth.

Chapter 4: A Geological and Chemical Context for the Origins of Life on Early Earth

Within the first billion years of Earth's history, the planet transformed from a hot, barren, and inhospitable landscape to an environment conducive to the emergence and persistence of life. This chapter will review the state of knowledge concerning early Earth's (Hadean/Eoarchean) geochemical environment, including the origin and composition of the planet's moon, crust, oceans, atmosphere, and organic content. It will also discuss abiotic geochemical cycling of the CHONPS elements and how these species could have been converted to biologically relevant building blocks, polymers, and chemical networks. Proposed environments for abiogenesis events are also described and evaluated. An understanding of the geochemical processes under which life may have emerged can better inform our assessment of the habitability of other worlds, the potential complexity that abiotic chemistry can achieve (which has implications for putative biosignatures), and the possibility for biochemistries that are vastly different from those on Earth.

Nitrogen Fixation by Benzene into Pyridine and Aniline in Water/Nitrogen Plasma

We demonstrated direct conversion of benzene into pyridine and aniline, assisted through exact mass measurements (m/z 80.0494, 93.0574, and 94.0651, respectively), through the interaction of benzene with water/nitrogen vapor plasma produced by corona discharge. Systematic analysis using a series of isotopic standards indicated that formation of pyridine and aniline occurred through the reaction between neutral benzene and reactive N+(OH2)2 in water/nitrogen plasma; exact mass measurements of products and intermediates supported this hypothesis. As the proportion of water vapor in plasma increased over time, the reaction proceeded from exclusive formation of protonated pyridine to formation of protonated aniline as the main product; theoretical simulations indicated that the presence of water vapor promoted proton migration to elicit formation of protonated aniline. The reactions we discovered suggest a new mechanism for direct nitrogen fixation.

Humid Evolution of Haze in the Atmosphere of Super-Earths in the Habitable Zone

Abstract Photochemical hazes are expected to form and significantly contribute to the chemical and radiative balance of exoplanets with relatively moderate temperatures, possibly in the habitable zone of their host star. In the presence of humidity, haze particles might thus serve as cloud condensation nuclei and trigger the formation of water droplets. In the present work, we are interested in the chemical impact of such a close interaction between photochemical hazes and humidity on the organic content composing the hazes and on the capacity to generate organic molecules with high prebiotic potential. For this purpose, we explore experimentally the sweet spot by combining N-dominated super-Earth exoplanets in agreement with Titan's rich organic photochemistry and humid conditions expected for exoplanets in habitable zones. A logarithmic increase with time is observed for the relative abundance of oxygenated species, with O-containing molecules dominating after 1 month only. The rapidity of the process suggests that the humid evolution of N-rich organic haze provides an efficient source of molecules with high prebiotic potential.

Synthesis of prebiotic organics from CO2 by catalysis with meteoritic and volcanic particles

The emergence of prebiotic organics was a mandatory step toward the origin of life. The significance of the exogenous delivery versus the in-situ synthesis from atmospheric gases is still under debate. We experimentally demonstrate that iron-rich meteoritic and volcanic particles activate and catalyse the fixation of CO₂, yielding the key precursors of life-building blocks. This catalysis is robust and produces selectively aldehydes, alcohols, and hydrocarbons, independent of the redox state of the environment. It is facilitated by common minerals and tolerates a broad range of the early planetary conditions (150-300 °C, ≲ 10-50 bar, wet or dry climate). We find that up to 6 × 10⁸ kg/year of prebiotic organics could have been synthesized by this planetary-scale process from the atmospheric CO₂ on Hadean Earth.

Reflections on the Origin and Early Evolution of the Genetic Code

Examination of the genetic code (GeCo) reveals that amino acids coded by (A/U) codons display a large functional spectrum and bind RNA whereas, except for Arg, those coded by (G/C) codons do not. From a stereochemical viewpoint, the clear preference for (A/U)-rich codons to be located at the GeCo half blocks suggests they were specifically determined. Conversely, the overall lower affinity of cognate amino acids for their (G/C)-rich anticodons points to their late arrival to the GeCo. It is proposed that i) initially the code was composed of the eight (A/U) codons; ii) these codons were duplicated when G/C nucleotides were added to their wobble positions, and three new codons with G/C in their first position were incorporated; and iii) a combination of A/U and G/C nucleotides progressively generated the remaining codons.

Why Were [GADV]-amino Acids and GNC Codons Selected and How Was GNC Primeval Genetic Code Established?

Correspondence relations between codons and amino acids are determined by genetic code. Therefore, genetic code holds a key of the life system composed of genes and protein. According to the GNC-SNS primitive genetic code hypothesis, which I have proposed, it is assumed that the genetic code originated from GNC code. In this article, first, it is discussed from a standpoint of primeval protein synthesis, why four [GADV]-amino acids were selected and used in the first GNC code. Next, it is explained from another standpoint of the most primitive anticodon-stem loop tRNAs (AntiC-SL tRNAs), how four GNCs were selected for the first codons. Furthermore, in the last section of this article, I will explain my idea of how the correspondence relations between four [GADV]-amino acids and four GNC codons were established. Namely, the origin and evolution of the genetic code was discussed comprehensively from several aspects of [GADV]-proteins, [GADV]-amino acids, GNC codons, and anticodon stem-loop tRNAs (AntiC-SL tRNAs), which relate each other to the origin of the genetic code, as integrating GNC code frozen-accident theory, coevolution theory, and adaptive theory on the origin of the genetic code.

Setting the geological scene for the origin of life and continuing open questions about its emergence

The origin of life is one of the most fundamental questions of humanity. It has been and is still being addressed by a wide range of researchers from different fields, with different approaches and ideas as to how it came about. What is still incomplete is constrained information about the environment and the conditions reigning on the Hadean Earth, particularly on the inorganic ingredients available, and the stability and longevity of the various environments suggested as locations for the emergence of life, as well as on the kinetics and rates of the prebiotic steps leading to life. This contribution reviews our current understanding of the geological scene in which life originated on Earth, zooming in specifically on details regarding the environments and timescales available for prebiotic reactions, with the aim of providing experimenters with more specific constraints. Having set the scene, we evoke the still open questions about the origin of life: did life start organically or in mineralogical form? If organically, what was the origin of the organic constituents of life? What came first, metabolism or replication? What was the time-scale for the emergence of life? We conclude that the way forward for prebiotic chemistry is an approach merging geology and chemistry, i.e., far-from-equilibrium, wet-dry cycling (either subaerial exposure or dehydration through chelation to mineral surfaces) of organic reactions occurring repeatedly and iteratively at mineral surfaces under hydrothermal-like conditions.

Natural Radioactivity and Chemical Evolution on the Early Earth: Prebiotic Chemistry and Oxygenation

It is generally recognized that the evolution of the early Earth was affected by an external energy source: radiation from the early Sun. The hypothesis about the important role of natural radioactivity, as a source of internal energy in the evolution of the early Earth, is considered and substantiated in this work. The decay of the long-lived isotopes ²³²Th, ²³⁸U, ²³⁵U, and ⁴⁰K in the Global Ocean initiated the oxygenation of the hydro- and atmosphere, and the abiogenesis. The content of isotopes in the ocean and the kinetics of their decay, the values of the absorbed dose and dose rate, and the efficiency of sea water radiolysis, as a function of time, were calculated. The ocean served as both a "reservoir" that collected components of the early atmosphere and products of their transformations, and a "converter" in which further chemical reactions of these compounds took place. Radical mechanisms were proposed for the formation of simple amino acids, sugars, and nitrogen bases, i.e., the key structures of all living things, and also for the formation of oxygen. The calculation results confirm the possible important role of natural radioactivity in the evolution of terrestrial matter, and the emergence of life.

Phosphorylation in liquid sulfur dioxide under prebiotically plausible conditions

In nature, organophosphates provide key functions such as information storage and transport, structural tasks, and energy transfer. Since condensations are unfavourable in water and nucleophilic attack at phosphate is kinetically inhibited, various abiogenesis hypotheses for the formation of organophosphate are discussed. Recently, the application of phosphites as phosphorylation agent showed promising results. However, elevated temperatures and additional reaction steps are required to obtain organophosphates. Here we show that in liquid sulfur dioxide, which acts as solvent and oxidant, efficient organophosphate formation is enabled. Phosphorous acid yields up to 32.6% 5' nucleoside monophosphate, 3.6% 5' nucleoside diphosphate, and the formation of nucleoside triphosphates and dinucleotides in a single reaction step at room temperature. In addition to the phosphorylation of organic compounds, we observed diserine formation. Thus, we suggest volcanic environments as reaction sites for biopolymer formation on Early Earth. Because of the simple recyclability of sulfur dioxide, the reaction is also interesting for synthesis chemistry.

A Physicochemical Consideration of Prebiotic Microenvironments for Self-Assembly and Prebiotic Chemistry

The origin of life on Earth required myriads of chemical and physical processes. These include the formation of the planet and its geological structures, the formation of the first primitive chemicals, reaction, and assembly of these primitive chemicals to form more complex or functional products and assemblies, and finally the formation of the first cells (or protocells) on early Earth, which eventually evolved into modern cells. Each of these processes presumably occurred within specific prebiotic reaction environments, which could have been diverse in physical and chemical properties. While there are resources that describe prebiotically plausible environments or nutrient availability, here, we attempt to aggregate the literature for the various physicochemical properties of different prebiotic reaction microenvironments on early Earth. We introduce a handful of properties that can be quantified through physical or chemical techniques. The values for these physicochemical properties, if they are known, are then presented for each reaction environment, giving the reader a sense of the environmental variability of such properties. Such a resource may be useful for prebiotic chemists to understand the range of conditions in each reaction environment, or to select the medium most applicable for their targeted reaction of interest for exploratory studies.

Synthesis and Characterization of Amino Acid Decyl Esters as Early Membranes for the Origins of Life

Understanding how membrane forming amphiphiles are synthesized and aggregate in prebiotic settings is required for understanding the origins of life on Earth 4 billion years ago. Amino acids decyl esters were prepared by dehydration of decanol and amino acid as a model for a plausible prebiotic reaction at two temperatures. Fifteen amino acids were tested with a range of side chain chemistries to understand the role of amino acid identity on synthesis and membrane formation. Products were analyzed using LC-MS as well as microscopy. All amino acids tested produced decyl esters, and some of the products formed membranes when rehydrated in ultrapure water. One of the most abundant prebiotic amino acids, alanine, was remarkably easy to get to generate abundant, uniform membranes, indicating that this could be a selection mechanism for both amino acids and their amphiphilic derivatives.

How Did Life Emerge in Chemically Complex Messy Environments?

One of the problems that make it difficult to solve the mystery of the origin of life is determining how life emerged in chemically complex messy environments on primitive Earth. In this article, the “chemically complex messy environments” that are focused on are a mixed state of various organic compounds produced via prebiotic means and accumulated on primitive earth. The five factors described below are thought to have contributed to opening the way for the emergence of life: (1) A characteristic inherent in [GADV]-amino acids, which are easily produced via prebiotic means. [GADV] stands for four amino acids, Gly [G], Ala [A], Asp [D] and Val [V], which are indicated by a one-letter symbol. (2) The protein 0th-order structure or a [GADV]-amino acid composition generating water-soluble globular protein with some flexibility, which can be produced even by the random joining of [GADV]-amino acids. (3) The formation of versatile [GADV]-microspheres, which can grow, divide and proliferate even without a genetic system, was the emergence of proto-life. (4) The [GADV]-microspheres with a higher proliferation ability than others were able to be selected. Proto-Darwin evolution made it possible to proceed forward to the creation of a core life system composed of the (GNC)_n gene, anticodon stem-loop tRNA or AntiC-SL tRNA (GNC genetic code), and [GADV]-protein. (5) Eventually, the first genuine life with a core life system emerged. Thus, the formation processes of [GADV]-protein and the (GNC)_n gene in chemically complex messy environments were the steps to the emergence of genuine life.

A Computational Quantum-Based Perspective on the Molecular Origins of Life’s Building Blocks

The search for the chemical origins of life represents a long-standing and continuously debated enigma. Despite its exceptional complexity, in the last decades the field has experienced a revival, also owing to the exponential growth of the computing power allowing for efficiently simulating the behavior of matter—including its quantum nature—under disparate conditions found, e.g., on the primordial Earth and on Earth-like planetary systems (i.e., exoplanets). In this minireview, we focus on some advanced computational methods capable of efficiently solving the Schro¨dinger equation at different levels of approximation (i.e., density functional theory)—such as ab initio molecular dynamics—and which are capable to realistically simulate the behavior of matter under the action of energy sources available in prebiotic contexts. In addition, recently developed metadynamics methods coupled with first-principles simulations are here reviewed and exploited to answer to old enigmas and to propose novel scenarios in the exponentially growing research field embedding the study of the chemical origins of life.

The Origin of Life: What Is the Question?

The question of the origin of life is a tenacious question that challenges many branches of science but is also extremely multifaceted. While prebiotic chemistry and micropaleontology reformulate the question as that of explaining the appearance of life on Earth in the deep past, systems chemistry and synthetic biology typically understand the question as that of demonstrating the synthesis of novel living matter from nonliving matter independently of historical constraints. The objective of this contribution is to disentangle the different readings of the origin-of-life question found in science. We identify three main dimensions along which the question can be differently constrained depending on context: historical adequacy, natural spontaneity, and similarity to life-as-we-know-it. We argue that the epistemic status of what needs to be explained-the explanandum-varies from approximately true when the origin-of-life question is the most constrained to entirely speculative when the constraints are the most relaxed. This difference in epistemic status triggers a shift in the nature of the origin-of-life question from an explanation-seeking question in the most constrained case to a fact-establishing question in the lesser-constrained ones. We furthermore explore how answers to some interpretations of the origin-of-life questions matter for other interpretations.

Water-Based Dynamic Depsipeptide Chemistry: Building Block Recycling and Oligomer Distribution Control Using Hydration-Dehydration Cycles

The high kinetic barrier to amide bond formation has historically placed narrow constraints on its utility in reversible chemistry applications. Slow kinetics has limited the use of amides for the generation of diverse combinatorial libraries and selection of target molecules. Current strategies for peptide-based dynamic chemistries require the use of nonpolar co-solvents or catalysts or the incorporation of functional groups that facilitate dynamic chemistry between peptides. In light of these limitations, we explored the use of depsipeptides: biorelevant copolymers of amino and hydroxy acids that would circumvent the challenges associated with dynamic peptide chemistry. Here, we describe a model system of N-(α-hydroxyacyl)-amino acid building blocks that reversibly polymerize to form depsipeptides when subjected to two-step evaporation-rehydration cycling under moderate conditions. The hydroxyl groups of these units allow for dynamic ester chemistry between short peptide segments through unmodified carboxyl termini. Selective recycling of building blocks is achieved by exploiting the differential hydrolytic lifetimes of depsipeptide amide and ester bonds, which we show are controllable by adjusting the solution pH, temperature, and time as well as the building blocks' side chains. We demonstrate that the polymerization and breakdown of the depsipeptides are facilitated by cyclic morpholinedione intermediates, and further show how structural properties dictate half-lives and product oligomer distributions using multifunctional building blocks. These results establish a cyclic mode of ester-based reversible depsipeptide formation that temporally separates the polymerization and depolymerization steps for the building blocks and may have implications for prebiotic polymer chemical evolution.

Stoichiometric network analysis in reaction networks yielding spontaneous mirror symmetry breaking in a prebiotic atmosphere

The generation of amino acid homochirality under prebiotic atmosphere conditions is a relevant issue in the study of the origin of life. This research is based on the production of amino acids via Strecker synthesis and how it is adjusted to the Kondepudi-Nelson autocatalytic model. The spontaneous mirror symmetry breaking (SMSB) of the new Kondepudi-Nelson-Strecker model, subject to two modifications (with Limited Enantioselective and Cross Inhibition), and also their combination were studied using the stoichiometric network analysis (SNA). In the calculations, the values obtained from the literature for alanine were considered. A total production of alanine of 7.56 × 10⁹ mol year^-1 was determined under prebiotic atmosphere conditions and starting from that value, the reaction rates for the models studied were estimated. Only the model with cross inhibition or achiral dimer formation is driven by stochastic fluctuations during SMSB. The stochastic fluctuation was estimated for a value of 2.619 × 10^-15 mol L^-1. This perturbation was sufficient to trigger SMSB. Finally, the results of SMSB were used to calculate the entropy production for the cross inhibition model.

The Prebiotic Kitchen: A Guide to Composing Prebiotic Soup Recipes to Test Origins of Life Hypotheses

“Prebiotic soup” often features in discussions of origins of life research, both as a theoretical concept when discussing abiological pathways to modern biochemical building blocks and, more recently, as a feedstock in prebiotic chemistry experiments focused on discovering emergent, systems-level processes such as polymerization, encapsulation, and evolution. However, until now, little systematic analysis has gone into the design of well-justified prebiotic mixtures, which are needed to facilitate experimental replicability and comparison among researchers. This paper explores principles that should be considered in choosing chemical mixtures for prebiotic chemistry experiments by reviewing the natural environmental conditions that might have created such mixtures and then suggests reasonable guidelines for designing recipes. We discuss both “assembled” mixtures, which are made by mixing reagent grade chemicals, and “synthesized” mixtures, which are generated directly from diversity-generating primary prebiotic syntheses. We discuss different practical concerns including how to navigate the tremendous uncertainty in the chemistry of the early Earth and how to balance the desire for using prebiotically realistic mixtures with experimental tractability and replicability. Examples of two assembled mixtures, one based on materials likely delivered by carbonaceous meteorites and one based on spark discharge synthesis, are presented to illustrate these challenges. We explore alternative procedures for making synthesized mixtures using recursive chemical reaction systems whose outputs attempt to mimic atmospheric and geochemical synthesis. Other experimental conditions such as pH and ionic strength are also considered. We argue that developing a handful of standardized prebiotic recipes may facilitate coordination among researchers and enable the identification of the most promising mechanisms by which complex prebiotic mixtures were “tamed” during the origin of life to give rise to key living processes such as self-propagation, information processing, and adaptive evolution. We end by advocating for the development of a public prebiotic chemistry database containing experimental methods (including soup recipes), results, and analytical pipelines for analyzing complex prebiotic mixtures.

The role of borosilicate glass in Miller-Urey experiment

We have designed a set of experiments to test the role of borosilicate reactor on the yielding of the Miller-Urey type of experiment. Two experiments were performed in borosilicate flasks, two in a Teflon flask and the third couple in a Teflon flask with pieces of borosilicate submerged in the water. The experiments were performed in CH4, N2, and NH3 atmosphere either buffered at pH 8.7 with NH4Cl or unbuffered solutions at pH ca. 11, at room temperature. The Gas Chromatography-Mass Spectroscopy results show important differences in the yields, the number of products, and molecular weight. In particular, a dipeptide, multi-carbon dicarboxylic acids, PAHs, and a complete panel of biological nucleobases form more efficiently or exclusively in the borosilicate vessel. Our results offer a better explanation of the famous Miller's experiment showing the efficiency of borosilicate in a triphasic system including water and the reduced Miller-Urey atmosphere.

A New Perspective on the Maillard Reaction and the Origin of Life

The Maillard reaction, a spontaneous 'one pot' reaction between amino acids and reducing sugars that occurs at low reactant concentrations and low temperatures, is a good candidate for having played a role in the origin of life on the Earth. In view of the probability that RNA and DNA were preceded by an evolutionary forerunner with a more straightforward prebiotic synthesis, it is a testament to the prescience of Oró and colleagues that, in 1975, they drew attention to the Maillard reaction, in particular evidence that melanoidin polymers (the end-product of the reaction) contain '…heterocyclic nitrogen compounds similar to the nitrogenous bases' (Nissenbaum in J Mol Evol 6:253-270, 1975). Indeed, reports of the Maillard reaction product, 2-Acetyl-6-(Hydroxymethyl)-5,6-Dihydro-4H-Pyridinone (AHDP), with a structure reminiscent of the pyrimidine nucleobase uracil, suggest the Maillard reaction might have played a key role in the synthesis of components of a proto-RNA polymer, with AHDP and two structurally related products predicted to be similar to uracil in the latter's ability to form non-standard base pair interactions. It is possible that the primary function of these interactions was to allow molecules such as AHDP to separate out of the prebiotic chemical clutter. If this were the case, catalysis, and coding-made possible by the polymerization of proto-nucleoside monomers into linear sequence strings-would have been evolving properties.

Electrochemically promoted oxidative α-cyanation of tertiary and secondary amines using cheap AIBN

The electrochemical α-cyanation of tertiary and secondary amines has been developed by using a cheap cyanide reagent, azobisisobutyronitrile (AIBN). The CN radical, generated through n-Bu₄NBr-meidated electrochemical oxidation, participates in a novel α-cyanation reaction under exogenous oxidant-free conditions.

Plausible Emergence and Self Assembly of a Primitive Phospholipid from Reduced Phosphorus on the Primordial Earth

How life arose on the primitive Earth is one of the biggest questions in science. Biomolecular emergence scenarios have proliferated in the literature but accounting for the ubiquity of oxidized (+ 5) phosphate (PO₄^3-) in extant biochemistries has been challenging due to the dearth of phosphate and molecular oxygen on the primordial Earth. A compelling body of work suggests that exogenous schreibersite ((Fe,Ni)₃P) was delivered to Earth via meteorite impacts during the Heavy Bombardment (ca. 4.1-3.8 Gya) and there converted to reduced P oxyanions (e.g., phosphite (HPO₃^2-) and hypophosphite (H₂PO₂^-)) and phosphonates. Inspired by this idea, we review the relevant literature to deduce a plausible reduced phospholipid analog of modern phosphatidylcholines that could have emerged in a primordial hydrothermal setting. A shallow alkaline lacustrine basin underlain by active hydrothermal fissures and meteoritic schreibersite-, clay-, and metal-enriched sediments is envisioned. The water column is laden with known and putative primordial hydrothermal reagents. Small system dimensions and thermal- and UV-driven evaporation further concentrate chemical precursors. We hypothesize that a reduced phospholipid arises from Fischer-Tropsch-type (FTT) production of a C8 alkanoic acid, which condenses with an organophosphinate (derived from schreibersite corrosion to hypophosphite with subsequent methylation/oxidation), to yield a reduced protophospholipid. This then condenses with an α-amino nitrile (derived from Strecker-type reactions) to form the polar head. Preliminary modeling results indicate that reduced phospholipids do not aggregate rapidly; however, single layer micelles are stable up to aggregates with approximately 100 molecules.

Plasma Modeling and Prebiotic Chemistry: A Review of the State-of-the-Art and Perspectives

We review the recent progress in the modeling of plasmas or ionized gases, with compositions compatible with that of primordial atmospheres. The plasma kinetics involves elementary processes by which free electrons ultimately activate weakly reactive molecules, such as carbon dioxide or methane, thereby potentially starting prebiotic reaction chains. These processes include electron–molecule reactions and energy exchanges between molecules. They are basic processes, for example, in the famous Miller-Urey experiment, and become relevant in any prebiotic scenario where the primordial atmosphere is significantly ionized by electrical activity, photoionization or meteor phenomena. The kinetics of plasma displays remarkable complexity due to the non-equilibrium features of the energy distributions involved. In particular, we argue that two concepts developed by the plasma modeling community, the electron velocity distribution function and the vibrational distribution function, may unlock much new information and provide insight into prebiotic processes initiated by electron–molecule collisions.

Constraints for Use of Ultraviolet Spectropolarimetry to Detect Chiral Amino Acids from Comets

Life is pervasive on planet Earth, but whether life is ubiquitous in the Galaxy and sustainable over timescales comparable to stellar evolution is unknown. Evidence suggests that life first appeared on Earth more than 3.77 Gyr ago, during a period of heavy meteoric bombardment. Amino acids, the building blocks of proteins, have been demonstrated to exist in interstellar ice. As such, the contribution of space-generated amino acids to those existing on Earth should be considered. However, detection of space amino acids is challenging. In this study, we used analytical data from several meteorites and in situ measurements of the comet 67P/Churyumov-Gerasimenko collected by the Rosetta probe to evaluate the detectability of alanine by ultraviolet spectropolarimetry. Alanine is the second-most abundant amino acid after glycine and is optically active. This chirality produces a unique signature that enables reliable identification of this amino acid using the imprint of optical rotatory dispersion (ORD) and circular dichroism (CD) in the ultraviolet spectrum (130-230 nm). Here, we show that the ORD signature could be detected in comets by using ultraviolet spectropolarimetric observations conducted at middle size space observatories. These observations can also provide crucial information for the study of sources of enantiomeric imbalance on Earth.

Evaluating Alternatives to Water as Solvents for Life: The Example of Sulfuric Acid

The chemistry of life requires a solvent, which for life on Earth is water. Several alternative solvents have been suggested, but there is little quantitative analysis of their suitability as solvents for life. To support a novel (non-terrestrial) biochemistry, a solvent must be able to form a stable solution of a diverse set of small molecules and polymers, but must not dissolve all molecules. Here, we analyze the potential of concentrated sulfuric acid (CSA) as a solvent for biochemistry. As CSA is a highly effective solvent but a reactive substance, we focused our analysis on the stability of chemicals in sulfuric acid, using a model built from a database of kinetics of reaction of molecules with CSA. We consider the sulfuric acid clouds of Venus as a test case for this approach. The large majority of terrestrial biochemicals have half-lives of less than a second at any altitude in Venus's clouds, but three sets of human-synthesized chemicals are more stable, with average half-lives of days to weeks at the conditions around 60 km altitude on Venus. We show that sufficient chemical structural and functional diversity may be available among those stable chemicals for life that uses concentrated sulfuric acid as a solvent to be plausible. However, analysis of meteoritic chemicals and possible abiotic synthetic paths suggests that postulated paths to the origin of life on Earth are unlikely to operate in CSA. We conclude that, contrary to expectation, sulfuric acid is an interesting candidate solvent for life, but further work is needed to identify a plausible route for life to originate in it.

Coenzymes and Their Role in the Evolution of Life

The evolution of coenzymes, or their impact on the origin of life, is fundamental for understanding our own existence. Having established reasonable hypotheses about the emergence of prebiotic chemical building blocks, which were probably created under palaeogeochemical conditions, and surmising that these smaller compounds must have become integrated to afford complex macromolecules such as RNA, the question of coenzyme origin and its relation to the evolution of functional biochemistry should gain new impetus. Many coenzymes have a simple chemical structure and are often nucleotide-derived, which suggests that they may have coexisted with the emergence of RNA and may have played a pivotal role in early metabolism. Based on current theories of prebiotic evolution, which attempt to explain the emergence of privileged organic building blocks, this Review discusses plausible hypotheses on the prebiotic formation of key elements within selected extant coenzymes. In combination with prebiotic RNA, coenzymes may have dramatically broadened early protometabolic networks and the catalytic scope of RNA during the evolution of life.

Prebiotic Reaction Networks in Water

A prevailing strategy in origins of life studies is to explore how chemistry constrained by hypothetical prebiotic conditions could have led to molecules and system level processes proposed to be important for life's beginnings. This strategy has yielded model prebiotic reaction networks that elucidate pathways by which relevant compounds can be generated, in some cases, autocatalytically. These prebiotic reaction networks provide a rich platform for further understanding and development of emergent "life-like" behaviours. In this review, recent advances in experimental and analytical procedures associated with classical prebiotic reaction networks, like formose and Miller-Urey, as well as more recent ones are highlighted. Instead of polymeric networks, i.e., those based on nucleic acids or peptides, the focus is on small molecules. The future of prebiotic chemistry lies in better understanding the genuine complexity that can result from reaction networks and the construction of a centralised database of reactions useful for predicting potential network evolution is emphasised.

A Few Experimental Suggestions Using Minerals to Obtain Peptides with a High Concentration of L-Amino Acids and Protein Amino Acids

The peptides/proteins of all living beings on our planet are mostly made up of 19 L-amino acids and glycine, an achiral amino acid. Arising from endogenous and exogenous sources, the seas of the prebiotic Earth could have contained a huge diversity of biomolecules (including amino acids), and precursors of biomolecules. Thus, how were these amino acids selected from the huge number of available amino acids and other molecules? What were the peptides of prebiotic Earth made up of? How were these peptides synthesized? Minerals have been considered for this task, since they can preconcentrate amino acids from dilute solutions, catalyze their polymerization, and even make the chiral selection of them. However, until now, this problem has only been studied in compartmentalized experiments. There are separate experiments showing that minerals preconcentrate amino acids by adsorption or catalyze their polymerization, or separate L-amino acids from D-amino acids. Based on the [GADV]-protein world hypothesis, as well as the relative abundance of amino acids on prebiotic Earth obtained by Zaia, several experiments are suggested. The main goal of these experiments is to show that using minerals it is possible, at least, to obtain peptides whose composition includes a high quantity of L-amino acids and protein amino acids (PAAs). These experiments should be performed using hydrothermal environments and wet/dry cycles. In addition, for hydrothermal environment experiments, it is very important to use one of the suggested artificial seawaters, and for wet/dry environments, it is important to perform the experiments in distilled water and diluted salt solutions. Finally, from these experiments, we suggest that, without an RNA world or even a pre genetic world, a small peptide set could emerge that better resembles modern proteins.

Atmospheric Nitrogen When Life Evolved on Earth

The amount of nitrogen (N₂) present in the atmosphere when life evolved on our planet is central for understanding the production of prebiotic molecules and, hence, is a fundamental quantity to constrain. Estimates of atmospheric molecular nitrogen partial surface pressures during the Archean, however, widely vary in the literature. In this study, we apply a model that combines newly gained insights into atmospheric escape, magma ocean duration, and outgassing evolution. Results suggest <420 mbar surface molecular nitrogen at the time when life originated, which is much lower compared with estimates in previous works and hence could impact our understanding of the production rate of prebiotic molecules such as hydrogen cyanide. Our revised values provide new input for atmospheric chamber experiments that simulate prebiotic chemistry on the early Earth. Our results that assume negligible nitrogen escape rates are in agreement with research based on solidified gas bubbles and the oxidation of iron in micrometeorites at 2.7 Gyr ago, which suggest that the atmospheric pressure was probably less than half the present-day value. Our results contradict previous studies that assume N₂ partial surface pressures during the Archean were higher than those observed today and suggest that, if the N₂ partial pressure were low in the Archean, it would likely be low in the Hadean as well. Furthermore, our results imply a biogenic nitrogen fixation rate from 9 to 14 Teragram N₂ per year (Tg N₂/year), which is consistent with modern marine biofixation rates and, hence, indicate an oceanic origin of this fixation process.

One-Pot Hydrogen Cyanide-Based Prebiotic Synthesis of Canonical Nucleobases and Glycine Initiated by High-Velocity Impacts on Early Earth

Chemical environments of young planets are assumed to be significantly influenced by impacts of bodies lingering after the dissolution of the protoplanetary disk. We explore the chemical consequences of impacts of these bodies under reducing planetary atmospheres dominated by carbon monoxide, methane, and molecular nitrogen. Impacts were simulated by using a terawatt high-power laser system. Our experimental results show that one-pot impact-plasma-initiated synthesis of all the RNA canonical nucleobases and the simplest amino acid glycine is possible in this type of atmosphere in the presence of montmorillonite. This one-pot synthesis begins with de novo formation of hydrogen cyanide (HCN) and proceeds through intermediates such as cyanoacetylene and urea.

The coenzyme/protein pair and the molecular evolution of life

Covering: up to 2020What was first? Coenzymes or proteins? These questions are archetypal examples of causal circularity in living systems. Classically, this "chicken-and-egg" problem was discussed for the macromolecules RNA, DNA and proteins. This report focuses on coenzymes and cofactors and discusses the coenzyme/protein pair as another example of causal circularity in life. Reflections on the origin of life and hypotheses on possible prebiotic worlds led to the current notion that RNA was the first macromolecule, long before functional proteins and hence DNA. So these causal circularities of living systems were solved by a time travel into the past. To tackle the "chicken-and-egg" problem of the protein-coenzyme pair, this report addresses this problem by looking for clues (a) in the first hypothetical biotic life forms such as protoviroids and the last unified common ancestor (LUCA) and (b) in considerations and evidence of the possible prebiotic production of amino acids and coenzymes before life arose. According to these considerations, coenzymes and cofactors can be regarded as very old molecular players in the origin and evolution of life, and at least some of them developed independently of α-amino acids, which here are evolutionarily synonymous with proteins. Discussions on "chicken-and-egg" problems open further doors to the understanding of evolution.

Redox state of Earth's magma ocean and its Venus-like early atmosphere

Exchange between a magma ocean and vapor produced Earth's earliest atmosphere. Its speciation depends on the oxygen fugacity (fO₂) set by the Fe³⁺/Fe²⁺ ratio of the magma ocean at its surface. Here, we establish the relationship between fO₂ and Fe³⁺/Fe²⁺ in quenched liquids of silicate Earth-like composition at 2173 K and 1 bar. Mantle-derived rocks have Fe³⁺/(Fe³⁺+Fe²⁺) = 0.037 ± 0.005, at which the magma ocean defines an fO₂ 0.5 log units above the iron-wüstite buffer. At this fO₂, the solubilities of H-C-N-O species in the magma ocean produce a CO-rich atmosphere. Cooling and condensation of H₂O would have led to a prebiotic terrestrial atmosphere composed of CO₂-N₂, in proportions and at pressures akin to those observed on Venus. Present-day differences between Earth's atmosphere and those of her planetary neighbors result from Earth's heliocentric location and mass, which allowed geologically long-lived oceans, in-turn facilitating CO₂ drawdown and, eventually, the development of life.

Primordial Radioactivity and Prebiotic Chemical Evolution: Effect of γ Radiation on Formamide-Based Synthesis

Although the effect of ionizing radiation on prebiotic chemistry is often overlooked, primordial natural radioactivity might have been an important source of energy for various chemical transformations. Estimates of the abundances of short-lived radionuclides on early Earth suggest that the primordial intensity of endogenous terrestrial radioactivity was up to 4 × 10³ times higher than it is today. Therefore, we assume that chemical substances in contact with radioactive rocks should therefore undergo radiolysis. The calculations are followed by research investigating the influence of ionizing γ radiation on basic prebiotic substances, including formamide mixed with various clays, which might have played the role of a catalyst and an agent that partially blocked radiation that was potentially destructive for the products. Our explorations of this effect have shown that the irradiation of formamide-clay mixtures at doses of ∼6 kGy produces significant amounts of urea (up to the maximal concentration of approximately 250 mg L^-1), which plays a role in HCN-based prebiotic chemistry.

A sensitive quantitative analysis of abiotically synthesized short homopeptides using ultraperformance liquid chromatography and time-of-flight mass spectrometry

In the origins of life field understanding the abiotic polymerization of simple organic monomers (e.g., amino acids) into larger biomolecules (e.g., oligopeptides), remains a seminal challenge. Recently, preliminary observations showed a limited set of peptides formed in the presence of the plausible prebiotic phosphorylating agent, diamidophosphate (DAP), highlighting the need for an analytical tool to critically evaluate the ability of DAP to induce oligomerization of simple organics under aqueous conditions. However, performing accurate and precise, targeted analyses of short oligopeptides remains a distinct challenge in the analytical chemistry field. Here, we developed a new technique to detect and quantitate amino acids and their homopeptides in a single run using ultraperformance liquid chromatography-fluorescence detection/time of flight mass spectrometry. Over an 8-minute retention time window, 18 target analytes were identified and quantitated, 16 of which were chromatographically separated at, or near baseline resolution. Compound identity was confirmed by accurate mass analysis using a 10 ppm mass tolerance window. This method featured limits of detection < 5 nM (< 1 fmol on column) and limits of quantitation (LOQs) <15 nM (< 3 fmol on column). The LODs and LOQs were upwards of ∼28x and ∼788x lower, respectively, than previous methods for the same analytes, highlighting the quantifiable advantages of this new method. Both detectors provided good quantitative linearity (R2 > 0.985) for all analytes spanning concentration ranges ∼3 - 4 orders of magnitude. We performed a series of laboratory experiments to investigate DAP-mediated oligomerization of amino acids and peptides and analyzed experimental products with the new method. DAP readily polymerized amino acids and peptides under a range of simulated environmental conditions. This research underscores the potential of DAP to have generated oligopeptides on the primordial Earth, enhancing prebiotic chemical diversity and complexity at or near the origin of life.

Impact-induced amino acid formation on Hadean Earth and Noachian Mars

Abiotic synthesis of biomolecules is an essential step for the chemical origin of life. Many attempts have succeeded in synthesizing biomolecules, including amino acids and nucleobases (e.g., via spark discharge, impact shock, and hydrothermal heating), from reduced compounds that may have been limited in their availabilities on Hadean Earth and Noachian Mars. On the other hand, formation of amino-acids and nucleobases from CO2 and N2 (i.e., the most abundant C and N sources on Earth during the Hadean) has been limited via spark discharge. Here, we demonstrate the synthesis of amino acids by laboratory impact-induced reactions among simple inorganic mixtures: Fe, Ni, Mg2SiO4, H2O, CO2, and N2, by coupling the reduction of CO2, N2, and H2O with the oxidation of metallic Fe and Ni. These chemical processes simulated the possible reactions at impacts of Fe-bearing meteorites/asteroids on oceans with a CO2 and N2 atmosphere. The results indicate that hypervelocity impact was a source of amino acids on the Earth during the Hadean and potentially on Mars during the Noachian. Amino acids formed during such events could more readily polymerize in the next step of the chemical evolution, as impact events locally form amino acids at the impact sites.

Unified prebiotically plausible synthesis of pyrimidine and purine RNA ribonucleotides

Theories about the origin of life require chemical pathways that allow formation of life's key building blocks under prebiotically plausible conditions. Complex molecules like RNA must have originated from small molecules whose reactivity was guided by physico-chemical processes. RNA is constructed from purine and pyrimidine nucleosides, both of which are required for accurate information transfer, and thus Darwinian evolution. Separate pathways to purines and pyrimidines have been reported, but their concurrent syntheses remain a challenge. We report the synthesis of the pyrimidine nucleosides from small molecules and ribose, driven solely by wet-dry cycles. In the presence of phosphate-containing minerals, 5'-mono- and diphosphates also form selectively in one-pot reactions. The pathway is compatible with purine synthesis, allowing the concurrent formation of all Watson-Crick bases.

Reconstruction and Characterization of Thermally Stable and Catalytically Active Proteins Comprising an Alphabet of ~ 13 Amino Acids

While extant organisms synthesize proteins using approximately 20 kinds of genetically coded amino acids, the earliest protein synthesis system is likely to have been much simpler, utilizing a reduced set of amino acids. However, which types of building blocks were involved in primordial protein synthesis remains unclear. Herein, we reconstructed three convergent sequences of an ancestral nucleoside diphosphate kinase, each comprising a 10 amino acid "alphabet," and found that two of these variants folded into soluble and stable tertiary structures. Therefore, an alphabet consisting of 10 amino acids contains sufficient information for creating stable proteins. Furthermore, re-incorporation of a few more amino acid types into the active site of the 10 amino acid variants improved the catalytic activity, although the specific activity was not as high as that of extant proteins. Collectively, our results provide experimental support for the idea that robust protein scaffolds can be built with a subset of the current 20 amino acids that might have existed abundantly in the prebiotic environment, while the other amino acids, especially those with functional sidechains, evolved to contribute to efficient enzyme catalysis.

On the Role of Water as a Catalyst in Prebiotic Chemistry

In this manuscript we provide computational support to the catalytic role of water in all kinds of pseudopericyclic reactions operating in the reductive acid cycle, as well as in other metabolic processes. Water catalysis is not limited to those reactions where simple translocation of hydrogen atoms occurs, such as those represented by NuH+E→Nu-EH general equation. Indeed, water catalysis is more general and extremely important in tautomerization reactions of the type HX-Y=Z→X=Y-ZH, which operate in the reductive citric acid cycle and metabolic processes. Moreover, the comprehensive theoretical study reported herein illustrates that these reactions appear to behave as authentic enzyme-catalyzed reactions showing Michaelis-Menten behavior, however with the abnormal singularity that the concentration of the catalytic "water clusters" of different length and nature must be taken as a huge number. Overall, the results presented are suggestive of the workability of the so-called "metabolism first" proposal in a hot water world, as water catalysis eliminates the dilution problem frequently associated to this proposal.

Chemistry of Abiotic Nucleotide Synthesis

The chemistry of abiotic nucleotide synthesis of RNA and DNA in the context of their prebiotic origins on early earth is a continuing challenge. How did (or how can) the nucleotides form and assemble from the small molecule inventories and under conditions that prevailed on early earth 3.5-4 billion years ago? This review provides a background and up-to-date progress that will allow the reader to judge where the field stands currently and what remains to be achieved. We start with a brief primer on the biological synthesis of nucleotides, followed by an extensive focus on the prebiotic formation of the components of nucleotides-either via the synthesis of ribose and the canonical nucleobases and then joining them together or by building both the conjoined sugar and nucleobase, part-by-part-toward the ultimate goal of forming RNA and DNA by polymerization. The review will emphasize that there are-and will continue to be-many more questions than answers from the synthetic, mechanistic, and analytical perspectives. We wrap up the review with a cautionary note in this context about coming to conclusions as to whether the problem of chemistry of prebiotic nucleotide synthesis has been solved.

CH3NO as a potential intermediate for early atmospheric HCN: a quantum chemical insight

Hydrogen cyanide (HCN) has played a central role in the production of several biological molecules under prebiotic conditions on primitive Earth. Previously, K. J. Zahnle (J. Geophys. Res.: Atmos., 1986, 91, 2819) and Tian et al. (Earth Planet. Sci. Lett., 2011, 308, 417) emphasized that HCN production in the early Earth's CH₄-rich atmosphere could have been possible through the reaction between active nitrogen atoms (N) and methane photolysis products. Here, we have proposed alternative pathways for the formation of early atmospheric HCN via the decomposition of CH₃NO as an intermediate. In the early Earth's O₂-free atmosphere, CH₃˙ could preferentially attach to NO, which was generated via early atmospheric volcanism or lightning and photochemical processes. We have quantum chemically explored both unimolecular and bimolecular decomposition pathways of CH₃NO via the assistance of another CH₃NO molecule and via H₂O, NH₃, HCl, HCOOH, HNO₃ and H₂SO₄ catalysis. Both energetic and kinetic analyses reveal that H₂SO₄ is more efficient in this regard than other atmospheric species. Overall, it has been suggested that the proposed bimolecular decomposition pathways might have been alternative pathways for the formation of HCN under certain conditions on prebiotic Earth, while the unimolecular decomposition of CH₃NO could lead to the formation of HCN in the high temperature volcanic environment on early Earth.

Ribose Selected as Precursor to Life

The chemical or prebiotic evolution referred also to as pre-Darwinian evolution describes chemical reactions up to the origin of a self-replicating system that was capable of Darwinian evolution. These chemical processes took place on Earth between about 3.7 and 4.5 billion years ago when cellular life came into being. The pre-Darwinian chemical evolution usually assumes hereditary elements, but does not regard them as self-organizing processes. Physical and chemical self-organization led to uninterrupted pre-Darwinian and Darwinian evolution. Thus, it is not justified to distinguish between different types of evolution. From the many possible solutions, evolution selected among those reactions that generated catalytic networks incorporating chemical sequence information and under gradually changing circumstances produced a reproducible and stable living system that adapted to these conditions. Major issues in this review involve prebiotic reactions leading to genetic evolution involving (1) abiotic sources of components of ribonucleotides and xenobiotic nucleotides, (2) formation of prebiotic RNA, (3) development of genetic RNA from random-sequence noncoding RNA, (4) transition from RNA World to DNA Empire, (5) the role of oxygenic photosynthesis in genetic transitions, and (6) hierarchical arrangement of processes involved in the optimized genetic system.

Enceladus: First Observed Primordial Soup Could Arbitrate Origin-of-Life Debate

A recent breakthrough publication has reported complex organic molecules in the plumes emanating from the subglacial water ocean of Saturn's moon Enceladus (Postberg et al., 2018, Nature 558:564-568). Based on detailed chemical scrutiny, the authors invoke primordial or endogenously synthesized carbon-rich monomers (<200 u) and polymers (up to 8000 u). This appears to represent the first reported extraterrestrial organics-rich water body, a conceivable milieu for early steps in life's origin ("prebiotic soup"). One may ask which origin-of-life scenario appears more consistent with the reported molecular configurations on Enceladus. The observed monomeric organics are carbon-rich unsaturated molecules, vastly different from present-day metabolites, amino acids, and nucleotide bases, but quite chemically akin to simple lipids. The organic polymers are proposed to resemble terrestrial insoluble kerogens and humic substances, as well as refractory organic macromolecules found in carbonaceous chondritic meteorites. The authors posit that such polymers, upon long-term hydrous interactions, might break down to micelle-forming amphiphiles. In support of this, published detailed analyses of the Murchison chondrite are dominated by an immense diversity of likely amphiphilic monomers. Our specific quantitative model for compositionally reproducing lipid micelles is amphiphile-based and benefits from a pronounced organic diversity. It thus contrasts with other origin models, which require the presence of very specific building blocks and are expected to be hindered by excess of irrelevant compounds. Thus, the Enceladus finds support the possibility of a pre-RNA Lipid World scenario for life's origin.

Possible Roles of Amphiphilic Molecules in the Origin of Biological Homochirality

A review. The question of homochirality is an intriguing problem in the field of chemistry, and is deeply related to the origin of life. Though amphiphiles and their supramolecular assembly have attracted less attention compared to biomacromolecules such as RNA and proteins, the lipid world hypothesis sheds new light on the origin of life. This review describes how amphiphilic molecules are possibly involved in the scenario of homochirality. Some prebiotic conditions relevant to amphiphilic molecules will also be described. It could be said that the chiral properties of amphiphilic molecules have various interesting features such as compositional information, spontaneous formation, the ability to exchange components, fission and fusion, adsorption, and permeation. This review aims to clarify the roles of amphiphiles regarding homochirality, and to determine what kinds of physical properties of amphiphilic molecules could have played a role in the scenario of homochirality.