Amino acids are essential for the synthesis of protein. Amino acids contain both amine (R–NH2) and carboxylic acid (R–COOH) functional groups, which help to understand the possible formation mechanism of life in the universe. Among the 20 types of amino acids, glycine (NH2CH2COOH) is known as the simplest non-essential amino acid. In the last 40 years, all surveys of NH2CH2COOH in the interstellar medium, especially in the star-formation regions, have failed at the millimetre and sub-millimetre wavelengths. We aimed to identify the possible precursors of NH2CH2COOH, because it is highly challenging to identify NH2CH2COOH in the interstellar medium. Many laboratory experiments have suggested that methylenimine (CH2NH) plays a key role as a possible precursor of NH2CH2COOH in the star-formation regions via the Strecker synthesis reaction. After spectral analysis using the local thermodynamic equilibrium (LTE) model, we successfully identified the rotational emission lines of CH2NH towards the hot molecular core G10.47+0.03 using the Atacama Compact Array (ACA). The estimated column density of CH2NH towards G10.47+0.03 is (3.40 ± 0.2) × 1015 cm−2 with a rotational temperature of 218.70 ± 20 K, which is estimated from the rotational diagram. The fractional abundance of CH2NH with respect to H2 towards G10.47+0.03 is 2.61 × 10−8. We found that the derived abundance of CH2NH agree fairly well with the existing two-phase warm-up chemical modelling abundance value of CH2NH. We discuss the possible formation pathways of CH2NH within the context of hot molecular cores, and we find that CH2NH is likely mainly formed via neutral–neutral gas-phase reactions of CH3 and NH radicals towards G10.47+0.03.

Comets are a source of prebiotic molecules that likely enriched the early Earth during the Late Heavy Bombardment period. Laboratory experiments that replicate cometary conditions may facilitate understanding of the chemical reactions and supplement observational studies of these icy bodies. Prebiotic compounds, such as formic acid and formaldehyde, have been observed in comets. Furthermore, these compounds can easily be formed in experimental models using a variety of gas combinations and energy sources. We conducted experimental cometary simulations using radiation chemistry tools to obtain insight into the possible fate of formic acid and formaldehyde. The main results suggest a redundant system, signifying that the irradiation of formic acid forms formaldehyde molecules and vice versa. This phenomenon ensures the permanence of prebiotic molecules in high-radiation environments. Additionally, the potential role of forsterite and graphite was explored in cometary simulations. Our experimental results show the differential formation of aldehydes and other carbonyl-containing compounds dependent on the mineral phase present.

Since their discovery, submarine hydrothermal vent systems have been pointed out as important places where chemical evolution on Earth could have occurred; and their role in the process has been highlighted. Similarly, some hypotheses have considered these systems in origin of life scenarios. In this way, many experiments have been developed, and the knowledge about these systems has increased. Due to their complexity, many experimental simulations have only included a few of the geochemical variables present in these environments, pressure and temperature. Other main variables have hardly been included, such as mineralogy, thermal and pH gradients, dissolved ions and/or redox reactions. As it has been understood, the dynamism and heterogeneity of these environments are huge, and it comprises different scales, from single vents to full hydrothermal fields. However, the vast majority of experiments focus on a specific part of these systems and do not include salinity, mineralogy and pH gradients. For this reason, in this paper, we pointed out some considerations about how this dynamism can be interpreted, and included in some models, as well their importance in prebiotic chemistry experiments and their extrapolations regarding the hypothesis about the origins of life.

The modification of minerals with metals can promote changes in their surface and, consequently, in their physicochemical properties. Minerals could have played an important role in the origin of life as they can protect molecules against degradation by radiation and hydrolysis, pre-concentrate molecules from dilute solutions and catalyse the formation of polymers. Thus, the current work studied the modification of montmorillonite with Cu2+ and Fe3+ ions. These modified montmorillonites were used to study the interaction with adenine dissolved in distilled water and artificial seawater 4.0 Gy (Gy = billion years ago). The most important result of this work is that the adsorption of adenine onto modified montmorillonites is a complex interaction among adenine, salts in seawater and Cu2+/Fe3+-montmorillonite (Cu2+/Fe3+-Mont) . The adsorption of Cu2+ and Fe3+ onto montmorillonite decreased its surface area and pore volume. The Sips isotherm model showed the best fit of the data and n values indicate that the adenine adsorption process was homogeneous. The highest adenine adsorption was obtained in artificial seawater 4.0 Gy onto Fe3+-Mont at 60°C and the lowest in distilled water or artificial seawater 4.0 Gy onto montmorillonite [montmorillonite washed with distilled water (Mont-STD)] at 60°C. Adenine adsorption onto Mont-STD/montmorillonite modified with 500 ml of 0.1 mol l−1 of CuCl2 and Fe3+-Mont was an exothermic process and an endothermic process, respectively. For all adsorptions ΔG was negative. The adsorption of adenine onto Fe3+-Mont was ruled out by entropy and the other samples by enthalpy and entropy, being a major contribution for Gibbs free energy from enthalpy. The Fourier transform-infrared data indicate that the interaction of adenine with minerals may occur through the NH2 functional group.

The origin of life from inanimate matter is still an open question, and our knowledge is still very limited. In this sense, prebiotic chemistry seeks to study and understand how chemical reactions may have contributed to the origin of life. Minerals are of great relevance to prebiotic chemistry, as they may have preconcentrated precursors of biomolecules or biomolecules from diluted solutions, provided protection for biomolecules against UV radiation and hydrolysis, catalysing their reactions and played the role of a primitive genetic code. Montmorillonite, a prebiotic mineral, was shown to be able to adsorb adenine and later also histidine. In addition, histidine adsorption did not displace adenine from the montmorillonite. Kinetic experiments showed that using a whole period of time (7 days) it was not possible to adjust the data to any mathematical kinetic model. Thus, the data were separated into four different adsorption ranges: range 1 (0–60 min), range 2 (60–4320 min), range 3 (4320–7200 min) and range 4 (7200–10 080 min). Range 1 showed adsorption that was too fast, meaning no variations in the adsorption data, and the data of range 3 did not fit in any model used in this work. Thus, range 2 (60–4320 min) and range 4 (7200–10 080 min) were analysed. The adsorption kinetics of histidine adsorption indicated two reaction steps, a quick step (60–4320 min), following the pseudo-first-order model, followed by a slower step (7200–10 080 min) of the pseudo-second order. With these results, isotherms were constructed with times of 1 h and 7 days. The results of the quick step (1 h) showed a reaction that was not thermodynamically favoured. For this time range, Gibbs energy values obtained ranged between 5 and 10 kJ mol−1 at temperatures of 20, 35 and 50°C, and the adsorption occurred due to the balance shift of increase in histidine concentrations. The isotherms of the slow step (7 days) presented negative values, showing a more favourable reaction with Gibbs energy values ranging between −5 and −11 kJ mol−1. The mathematical modelling of the data indicates that seawater ions are crucial in the adsorption process. Thus, the study provided essential information for prebiotic chemistry, showing that time and the reaction medium should always be taken into account.

The formation mechanism of linear and isopropyl cyanide (hereafter n-PrCN and i-PrCN, respectively) in the interstellar medium (ISM) has been proposed from the reaction between some previously detected small cyanides/cyanide radicals and hydrocarbons/hydrocarbon radicals. n-PrCN and i-PrCN are nitriles therefore, they can be precursors of amino acids via Strecker synthesis. The chemistry of i-PrCN is especially important since it is the first and only branched molecule in ISM, hence, it could be a precursor of branched amino acids such as leucine, isoleucine, etc. Therefore, both n-PrCN and i-PrCN have significant astrobiological importance. To study the formation of n-PrCN and i-PrCN in ISM, quantum chemical calculations have been performed using density functional theory at the MP2/6-311++G(2d,p)//M062X/6-311+G(2d,p) level. All the proposed reactions have been studied in the gas phase and the interstellar water ice. It is found that reactions of small cyanide with hydrocarbon radicals result in the formation of either large cyanide radicals or ethyl and vinyl cyanide, both of which are very important prebiotic interstellar species. They subsequently react with the radicals CH2 and CH3 to yield n-PrCN and i-PrCN. The proposed reactions are efficient in the hot cores of SgrB2 (N) (where both n-PrCN and i-PrCN were detected) due to either being barrierless or due to the presence of a permeable entrance barrier. However, the formation of n-PrCN and i-PrCN from the ethyl and vinyl cyanide always has an entrance barrier impermeable in the dark cloud; therefore, our proposed pathways are inefficient in the deep regions of molecular clouds. It is also observed that ethyl and vinyl cyanide serve as direct precursors to n-PrCN and i-PrCN and their abundance in ISM is directly related to the abundance of both isomers of propyl cyanide in ISM. In all the cases, reactions in the ice have smaller barriers compared to their gas-phase counterparts.

Hydrogen cyanide (HCN) is considered a fundamental molecule in prebiotic chemistry experiments due to the fact that it could have an important role as raw material to form more complex molecules, as well as it could be an intermediate molecule in chemical reactions. However, the primitive scenarios in which this molecule might be available have been widely discussed. Hydrothermal systems have been considered as abiotic reactors and ideal niches for chemical evolution. Nevertheless, several experiments have shown that high temperatures and pressures could be adverse to the stability of organic molecules. Thus, it is necessary to carry out systematic experiments to study the synthesis, stability and fate of organic molecules in hydrothermal scenarios. In this work, we performed experiments focused on the stability and fate of HCN under a simple hydrothermal system scenario: the thermolysis of HCN at 100°C, at acidic and basic pH and in the presence of Mg-montmorillonite. Furthermore, we analysed the products from HCN thermolysis and highlighted the role of these chemical species as prebiotic molecules under a hydrothermal scenario.

Life originated on Earth possibly as a physicochemical process; thus, geological environments and their hypothetical characteristics on early Earth are essential for chemical evolution studies. Also, it is necessary to consider the energy sources that were available in the past and the components that could have contributed to promote chemical reactions. It has been proposed that the components could have been mineral surfaces. The aim of this work is to determine the possible role of mineral surfaces on chemical evolution, and to study of the stability of relevant molecules for metabolism, such as α-ketoglutaric acid (α-keto acid, Krebs cycle participant), using ionizing radiation and thermal energy as energy sources and mineral surfaces to promote chemical reactions. Preliminary results show α-ketoglutaric acid can be relatively stable at the simulated conditions of an impact-generated hydrothermal system; thus, those systems might have been plausible environments for chemical evolution on Earth.

In this work, the effect of γ-radiation on the decomposition of adenine dissolved in distilled water, saline solutions and artificial seawater was studied. As the composition of the major cations and anions of artificial seawater probably better resembles the composition of seawater on the Earth 4.0 billion years ago, this seawater was named artificial seawater 4.0 Ga. The main finding in this work is that artificial seawater 4.0 Ga demonstrated a better protective effect of adenine against γ-radiation. In addition, artificial seawater 4.0 Ga showed that adenine had no changes in pH after radiation exposure and the minor radiation-chemical yield G. The radiolysis of adenine promoted modifications in Fourier-transform infrared spectra. The deconvolution of some bands demonstrated the formation of a new frequency at 1713 cm−1. High performance liquid chromatography-mass detected a product of decomposition with 151 atomic units. Using the geometry optimization and simulated vibrational spectra it was possible to show that the main species formed are hydroxyl and oxide modified adenine. The data point to the formation of hydroxyl-adenine and adenine Nx-oxide. These products have biological relevance and could be available for chemical evolution.

We use the critical step model to study the major transitions in evolution on Earth. We find that a total of five steps represents the most plausible estimate, in agreement with previous studies, and use the fossil record to identify the potential candidates. We apply the model to Earth-analogs around stars of different masses by incorporating the constraints on habitability set by stellar physics including the habitable zone lifetime, availability of ultraviolet radiation for prebiotic chemistry, and atmospheric escape. The critical step model suggests that the habitability of Earth-analogs around M-dwarfs is significantly suppressed. The total number of stars with planets containing detectable biosignatures of microbial life is expected to be highest for K-dwarfs. In contrast, we find that the corresponding value for intelligent life (technosignatures) should be highest for solar-mass stars. Thus, our work may assist in the identification of suitable targets in the search for biosignatures and technosignatures.

Formaldehyde is a precursor of sugars, which are compounds essential in all forms of life and a necessary molecule for prebiotic processes. This work focuses on evaluating the stability of formaldehyde exposed to a high radiation field simulating prebiotic conditions on primitive Earth, such as the ocean or shallow waters. Formaldehyde may have been formed from reactions in the atmosphere and from rainout processes reached water bodies. In our experiments, we employed γ radiation and found that formaldehyde was labile towards radiation and decomposed even at low irradiation doses due to the fact that aldehyde/hydrate groups present in formaldehyde structure are very reactive under irradiation. However, after exposing this molecule to several doses of irradiation, we detected the formation of formic acid and glycolaldehyde – both of which are of prebiotic interest. We also observed formaldehyde regeneration by one of its radiolytic products: formic acid.

We study the prospects for life on planets with subsurface oceans, and find that a wide range of planets can exist in diverse habitats with ice envelopes of moderate thickness. We quantify the energy sources available to these worlds, the rate of production of prebiotic compounds, and assess their potential for hosting biospheres. Life on these planets is likely to face challenges, which could be overcome through a combination of different mechanisms. We estimate the number of such worlds, and find that they may outnumber rocky planets in the habitable zone of stars by a few orders of magnitude.

The role of manganese oxides in concentrating organic moieties and offering catalytic activity for prebiotic reactions is investigated by studying their interaction with different aromatic amines such as aniline, p-chloroaniline, p-toluidine and p-anisidine. For all amines, metal oxides showed highest adsorption at neutral pH. The order of their adsorption capacity and affinity as revealed by the Langmuir constants was found to be manganosite (MnO) > bixbyite (Mn2O3) > hausmannite (Mn3O4) > and pyrolusite (MnO2). At alkaline pH, these manganese oxides offered their surfaces for oxidation of amines to form coloured oligomers. Analysis of the oxidation products by gas chromatography–mass spectrometry showed the formation of a dimer from p-anisidine and p-chloroaniline, while a trimer and tetramer is formed from p-toluidine and aniline, respectively. A reaction mechanism is proposed for the formation of the oligomers. While field-emission scanning electron microscopic studies confirm the binding phenomenon, the Fourier transform infrared spectroscopy analysis suggests that the mechanism of binding of amines on the manganese oxides was primarily electrostatic. The adsorption behaviour of the studied aromatic amines followed the order: p-anisidine > p-toluidine > aniline > p-chloroaniline, which is related to the basicities and structure of the amines. Our studies confirmed the significance of the role of manganese oxides in prebiotic chemistry.

Kepler observations suggest that G-type stars produce powerful flares suggesting that the early Earth may also have been exposed to frequent and energetic solar explosive events generated by the young Sun. We show that powerful coronal mass ejection (CME) events associated with superflares impacting the Earth magnetosphere with a frequency of 1 event/day. What was the impact of superflares, CMEs and associated solar energetic particle (SEPs) events on the atmospheric erosion of the young Earth and habitability? In this paper we discuss our three-dimensional (3D) magnetohydrodynamic (MHD) simulations that show that frequent and energetic CMEs from the early Sun continuously destroyed the sub-solar parts of Earth's magnetosphere at heights < 1.25 RE. This suggests that CME shock accelerated energetic protons are capable of penetrating into the polar cap region and breaking atmospheric molecular nitrogen, the major ingredient of the early Earth atmosphere, into atomic nitrogen. Photo-collisional dissociation of molecular nitrogen and carbon dioxide creates reactive chemistry that efficiently produces nitrous oxide and hydrogen cyanide, the essential molecule in prebiotic life chemistry. This raises an possibility that frequent super-CMEs could serve as a potential catalyst for the origin of life on early Earth.

This work investigates the consequences on the diverse number of chemical species in a pre-biotic terrestrial aqueous environment endowed with an amino acid source induced by the spontaneous build-up of catalytically active polypeptides from amino acid monomers. The assumed probability that a randomly formed polypeptide exhibits catalytic properties is dependent on constraining both the chemical identity and the position of a fraction of the amino acid residues. Within this hypothesis, and using values of the average length n of the catalytic polypeptides about one half of the present-day enzymes, the stationary-state concentration of the catalytically active polypeptides is ≈10−30 −10−19 M, and the ratio of the concentration of a product of a catalytic process to the initial concentration of the corresponding substrate is predicted to be ≈10−6−105. Matching the mean life of each catalytic polypeptide to the mean life of its substrate (λ ≈ ω) is only possible by significantly raising the intensity of the source of the amino acid monomers. Under these hypothetical optimal conditions, the mean lives of the catalytic polypeptides and their substrates have values ω−1 ≈ λ−1 ≈10 yr and the asymptotic concentration of each product is of the same order of magnitude as the concentration of the substrate. In all cases the catalytic efficiency necessary to form the active peptides takes the typical values of present-day enzymes.

The adsorption of amino acids onto minerals in prebiotic seas may have played an important role for their protection against hydrolysis and formation of polymers. In this study, we show that the adsorption of the prebiotic amino acids, glycine (Gly), α-alanine (α-Ala) and β-alanine (β-Ala), onto Na+-montmorillonite was dependent on salinity and pH. Specifically, adsorption decreased from 58.3–88.8 to 0–48.9% when salinity was increased from 10 to 100–150% of modern seawater. This result suggests reduced amino acid adsorption onto minerals in prebiotic seas, which may have been even more saline than the tested conditions. Amino acids also formed complexes with metals in seawater, affecting metal adsorption onto Na+-montmorillonite, and amino acid adsorption was enhanced when added before Na+-montmorillonite was exposed to high saline solutions. Also, the dissolution of Na+-montmorillonite was reduced in the presence of amino acids, with β-Ala being the most effective. Thus, prebiotic chemistry experiments should also consider the integrity of minerals in addition to their adsorption capacity.

Charged dust grains in the atmospheres of exoplanets may play a key role in the formation of prebiotic molecules, necessary to the origin of life. Dust grains submerged in an atmospheric plasma become negatively charged and attract a flux of ions that are accelerated from the plasma. The energy of the ions upon reaching the grain surface may be sufficient to overcome the activation energy of particular chemical reactions that would be unattainable via ion and neutral bombardment from classical, thermal excitation. As a result, prebiotic molecules or their precursors could be synthesized on the surface of dust grains that form clouds in exoplanetary atmospheres. This paper investigates the energization of the plasma ions, and the dependence on the plasma electron temperature, in the atmospheres of substellar objects such as gas giant planets. Calculations show that modest electron temperatures of ≈1 eV (≈104 K) are enough to accelerate ions to sufficient energies that exceed the activation energies required for the formation of formaldehyde, ammonia, hydrogen cyanide and the amino acid glycine.

In the present work, the interactions between forsterite-91 with distilled water and forsterite-91 with artificial seawater were studied at two pHs (2.0 and 8.0) using different techniques. A large increase in pH was observed for samples incubated at an initially acidic pH (2.0) due to the dissolution of forsterite-91 in distilled water and artificial seawater. Thus, in acidic hydrothermal vents, an increase in the amount of hydrocarbons and magnetite should be expected due to the release of Fe(II). The pHPZC decreased and the pHIEP increased when forsterite-91 was treated with distilled water and artificial seawater. The ions from the artificial seawater had an effect on zeta potential. Scanning electron microscopy (SEM) images and X-ray diffractograms showed halite in the samples of forsterite-91 mixed with artificial seawater. The presence of halite or adsorption of ions on the surface of forsterite-91 could affect the synthesis of magnetite and hydrocarbons in hydrothermal vents, due to a decrease in the dissolution rates of forsterite-91. The dissolution of forsterite-91 yields low concentrations of Fe(III) and Mn(II) as detected by electron paramagnetic resonance (EPR) spectroscopy. Microanalysis of forsterite-91 showed a higher amount of Mn, with an oxidation that was likely not +II, as Mn in supernatant solutions was only detected by EPR spectroscopy after mixing with artificial seawater at pH 2.0. As Fe(III) and Mn(II) are catalyst constituents of magnetite and manganese oxide, respectively, their presence is important for synthesis in hydrothermal vents. Etch pits were observed only in the forsterite-91 sample mixed with distilled water at pH 8.0. Na, Cl, S, Ca and K were detected in the samples mixed with artificial seawater by SEM–EDS. Si, Mg, Fe and Al were detected in almost all supernatant samples due to forsterite-91 dissolution. Cr was not dissolved in the experiments, thus Cr in the mineral could serve as an effective catalyst for Fischer Tropsch Types (FTT) reactions in hydrothermal vent systems. X-ray diffractograms of the original forsterite-91 also showed peaks arising from zeolites and clinochlore. After the samples were treated with artificial seawater, X-ray diffractograms showed the dissolution of zeolite. Experiments should be performed in the natural environment to verify the potential for zeolites to act as a catalyst in hydrothermal vents.

This study investigated the synthesis of goethite under conditions resembling those of the prebiotic Earth. The artificial seawater used contains all the major elements as well as amino acids (α-Ala, β-Ala, Gly, Cys, AIB) that could be found on the prebiotic Earth. The spectroscopic methods (FT-IR, EPR, Raman), scanning electron microscopy (SEM) and X-ray diffraction showed that in any condition Gly and Cys favoured the formation of goethite, artificial seawater plus β-Ala and distilled water plus AIB favoured the formation of hematite and for the other synthesis a mixture of goethite and hematite were obtained. Thus in general no protein amino acids (β-Ala, AIB) favoured the formation of hematite. As shown by surface enhanced Raman spectroscopy (SERS) spectra the interaction between Cys and Fe3+ of goethite is very complex, involving decomposition of Cys producing sulphur, as well as interaction of carboxylic group with Fe3+. SERS spectra also showed that amino/CN and C-CH3 groups of α-Ala are interacting with Fe3+ of goethite. For the other samples the shifting of several bands was observed. However, it was not possible to say which amino acid groups are interacting with Fe3+. The pH at point of zero charge of goethites increased with artificial seawater and decreased with amino acids. SEM images showed when only goethite was synthesized the images of the samples were acicular and when only hematite was synthesized the images of the samples were spherical. SEM images for the synthesis of goethite with Cys were spherical crystal aggregates with radiating acicular crystals. The highest resonance line intensities were obtained for the samples where only hematite was obtained. Electron paramagnetic resonance (EPR) and Mössbauer spectra showed for the synthesis of goethite with artificial seawater an isomorphic substitution of iron by seawater cations. Mössbauer spectra also showed that for the synthesis goethite in distilled water plus Gly only goethite was synthesized and in artificial seawater plus Cys a doublet due to interaction of iron with artificial seawater/Cys was observed. It should be pointed out that EPR spectroscopy did not show the interaction of iron with artificial seawater/Cys.

The adsorption of organic molecules on mineral matrices might have played a fundamental role in processes that led to the emergence of life. We investigated the adsorption properties of the nucleobases adenine, cytosine, uracil and hypoxanthine on magnesium oxide (MgO), determining the single solute batch equilibrium adsorption isotherms. Langmuir-type isotherms were fitted to data, assuming a rapid reversible equilibration of adsorption, demonstrated effectively through desorption experiments. The Langmuir equilibrium adsorption constant K and the amount of the solute per unit of adsorbent mass necessary to complete the monolayer b were calculated. The results indicate that MgO is a good adsorbent for nucleobases (adenine > uracil > hypoxantine > cytosine), suggesting a role of metal oxides in concentrating biomolecules in prebiotic conditions that might have favoured the passage from geochemistry to biochemistry.