Computational Study on the Water Corrosion Process at Schreibersite (Fe2NiP) Surfaces: from Phosphide to Phosphates

Phosphorus (P) is a fundamental element for whatever form of life, in the same way as the other biogenic macroelements (SONCH). The prebiotic origin of P is still a matter of debate, as the phosphates present on earth are trapped in almost insoluble solid matrixes (apatites) and, therefore, hardly available for inclusion in living systems in the prebiotic era. The most accepted theories regard a possible exogenous origin during the Archean Era, through the meteoritic bombardment, when tons of reactive P in the form of phosphide ((Fe,Ni)3P, schreibersite mineral) reached the primordial earth, reacting with water and providing oxygenated phosphorus compounds (including phosphates). In the last 20 years, laboratory experiments demonstrated that the corrosion process of schreibersite by water indeed leads to reactive phosphates that, in turn, react with other biological building blocks (nucleosides and simple sugars) to form more complex molecules (nucleotides and complex sugars). In the present paper, we study the water corrosion of different crystalline surfaces of schreibersite by means of periodic DFT (density functional theory) simulations. Our results show that water adsorbs molecularly on the most stable (110) surface but dissociates on the less stable (001) one, giving rise to further reactivity. Indeed, subsequent water adsorptions, up to the water monolayer coverage, show that, on the (001) surface, iron and nickel atoms are the first species undergoing the corrosion process and, in a second stage, the phosphorus atoms also get involved. When adsorbing up to three and four water molecules per unit cell, the most stable structures found are the phosphite and phosphate forms of phosphorus, respectively. Simulation of the vibrational spectra of the considered reaction products revealed that the experimental band at 2423 cm-1 attributed to the P-H stretching frequency is indeed predicted for a phosphite moiety attached to the schreibersite (001) surface upon chemisorption of up to three water molecules.

Prebiotic Chemistry of Phosphite: Mild Thermal Routes to Form Condensed-P Energy Currency Molecules Leading Up to the Formation of Organophosphorus Compounds

The in-fall of meteorites and interstellar dust particles during the Hadean-Archean heavy bombardment may have provided the early Earth with various reduced oxidation state phosphorus compounds and minerals, including phosphite (HPO32-)([Pi(III)]). The ion phosphite ([Pi(III)])has been postulated to be ubiquitous on the early Earth and consequently could have played a role in the emergence of organophosphorus compounds and other prebiotically relevant P species such as condensed P compounds, e.g., pyrophosphite ([PPi(III)]) and isohypophosphate ([PPi(III-V)]). In the present study, we show that phosphite ([Pi(III)]) oxidizes under mild heating conditions (e.g., wet-dry cycles and a prebiotic scenario mimicking a mildly hot-evaporating/drying pool on the early Earth at 78-83 °C) in the presence of urea and other additives, resulting in changes to orthophosphate ([Pi(V)]) alongside the formation of reactive condensed P compounds (e.g., pyrophosphite ([PPi(III)]) and isohypophosphate ([PPi(III-V)])) through a one-pot mechanism. Additionally, we also show that phosphite ([Pi(III)]) and the condensed P compounds readily react with organics (nucleosides and organic alcohol) to form organophosphorus compounds.

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.

Results of an Eight-Year Extraction of Phosphorus Minerals within the Seymchan Meteorite

In-fall of extraterrestrial material including meteorites and interstellar dust particles during the late heavy bombardment are known to have brought substantial amounts of reduced oxidation-state phosphorus to the early Earth in the form of siderophilic minerals, e.g., schreibersite ((FeNi)₃P). In this report, we present results on the reaction of meteoritic phosphide minerals in the Seymchan meteorite in ultrapure water for 8 years. The ions produced during schreibersite corrosion (phosphite, hypophosphate, pyrophosphate, and phosphate) are stable and persistent in aqueous solution over this timescale. These results were also compared with the short-term corrosion reactions of the meteoritic mineral schreibersite's synthetic analog Fe₃P in aqueous and non-aqueous solutions (ultrapure water and formamide). This finding suggests that the reduced-oxidation-state phosphorus (P) compounds including phosphite could be ubiquitous and stable on the early Earth over a long span of time and such compounds could be readily available on the early Earth.

A material-based panspermia hypothesis: The potential of polymer gels and membraneless droplets

The Panspermia hypothesis posits that either life's building blocks (molecular Panspermia) or life itself (organism-based Panspermia) may have been interplanetarily transferred to facilitate the origins of life (OoL) on a given planet, complementing several current OoL frameworks. Although many spaceflight experiments were performed in the past to test for potential terrestrial organisms as Panspermia seeds, it is uncertain whether such organisms will likely "seed" a new planet even if they are able to survive spaceflight. Therefore, rather than using organisms, using abiotic chemicals as seeds has been proposed as part of the molecular Panspermia hypothesis. Here, as an extension of this hypothesis, we introduce and review the plausibility of a polymeric material-based Panspermia seed (M-BPS) as a theoretical concept, where the type of polymeric material that can function as a M-BPS must be able to: (1) survive spaceflight and (2) "function", i.e., contingently drive chemical evolution toward some form of abiogenesis once arriving on a foreign planet. We use polymeric gels as a model example of a potential M-BPS. Polymeric gels that can be prebiotically synthesized on one planet (such as polyester gels) could be transferred to another planet via meteoritic transfer, where upon landing on a liquid bearing planet, can assemble into structures containing cellular-like characteristics and functionalities. Such features presupposed that these gels can assemble into compartments through phase separation to accomplish relevant functions such as encapsulation of primitive metabolic, genetic and catalytic materials, exchange of these materials, motion, coalescence, and evolution. All of these functions can result in the gels' capability to alter local geochemical niches on other planets, thereby allowing chemical evolution to lead to OoL events.

Water Interaction with Fe2NiP Schreibersite (110) Surface: a Quantum Mechanical Atomistic Perspective

Phosphorus is an element of primary importance for all living creatures, being present in many biological activities in the form of phosphate (PO₄ ^3-). However, there are still open questions about the origin of this specific element and on the transformation that allowed it to be incorporated in biological systems. The most probable source of prebiotic phosphorus is the intense meteoritic bombardment during the Archean era, a few million years after the solar system formation, which brought tons of iron-phosphide materials (schreibersite) on the early Earth crust. It was recently demonstrated that by simple wetting/corrosion processes from this material, various oxygenated phosphorus compounds are produced. In the present work, the wetting process of schreibersite (Fe₂NiP) was studied by computer simulations using density functional theory, with the PBE functional supplemented with dispersive interactions through a posteriori empirical correction. To start disentangling the complexity of the system, only the most stable (110) surface of Fe₂NiP was used simulating different water coverages, from which structures, water binding energies, and vibrational spectra have been predicted. The computed (ana-)harmonic infrared spectra have been compared with the experimental ones, thus, confirming the validity of the adopted methodology and models.

Lightning strikes as a major facilitator of prebiotic phosphorus reduction on early Earth

When hydrated, phosphides such as the mineral schreibersite, (Fe,Ni)₃P, allow for the synthesis of important phosphorus-bearing organic compounds. Such phosphides are common accessory minerals in meteorites; consequently, meteorites are proposed to be a main source of prebiotic reactive phosphorus on early Earth. Here, we propose an alternative source for widespread phosphorus reduction, arguing that lightning strikes on early Earth potentially formed 10-1000 kg of phosphide and 100-10,000 kg of phosphite and hypophosphite annually. Therefore, lightning could have been a significant source of prebiotic, reactive phosphorus which would have been concentrated on landmasses in tropical regions. Lightning strikes could likewise provide a continual source of prebiotic reactive phosphorus independent of meteorite flux on other Earth-like planets, potentially facilitating the emergence of terrestrial life indefinitely.

Prebiotic Peptide Bond Formation Through Amino Acid Phosphorylation. Insights from Quantum Chemical Simulations

Condensation reactions between biomolecular building blocks are the main synthetic channels to build biopolymers. However, under highly diluted prebiotic conditions, condensations are thermodynamically hampered since they release water. Moreover, these reactions are also kinetically hindered as, in the absence of any catalyst, they present high activation energies. In living organisms, in the formation of peptides by condensation of amino acids, this issue is overcome by the participation of adenosine triphosphate (ATP), in which, previous to the condensation, phosphorylation of one of the reactants is carried out to convert it as an activated intermediate. In this work, we present for the first time results based on density functional theory (DFT) calculations on the peptide bond formation between two glycine (Gly) molecules adopting this phosphorylation-based mechanism considering a prebiotic context. Here, ATP has been modeled by a triphosphate (TP) component, and different scenarios have been considered: (i) gas-phase conditions, (ii) in the presence of a Mg²⁺ ion available within the layer of clays, and (iii) in the presence of a Mg²⁺ ion in watery environments. For all of them, the free energy profiles have been fully characterized. Energetics derived from the quantum chemical calculations indicate that none of the processes seem to be feasible in the prebiotic context. In scenarios (i) and (ii), the reactions are inhibited due to unfavorable thermodynamics associated with the formation of high energy intermediates, while in scenario (iii), the reaction is inhibited due to the high free energy barrier associated with the condensation reactions. As a final consideration, the role of clays in this TP-mediated peptide bond formation route is advocated, since the interaction of the phosphorylated intermediate with the internal clay surfaces could well favor the reaction free energies.

Origin of alkylphosphonic acids in the interstellar medium

For decades, the source of phosphorus incorporated into Earth's first organisms has remained a fundamental, unsolved puzzle. Although contemporary biomolecules incorporate P(+V) in their phosphate moieties, the limited bioavailability of phosphates led to the proposal that more soluble P(+III) compounds served as the initial source of phosphorus. Here, we report via laboratory simulation experiments that the three simplest alkylphosphonic acids, soluble organic phosphorus P(+III) compounds, can be efficiently generated in interstellar, phosphine-doped ices through interaction with galactic cosmic rays. This discovery opens a previously overlooked avenue into the formation of key molecules of astrobiological significance and untangles basic mechanisms of a facile synthesis of phosphorus-containing organics in extraterrestrial ices, which can be incorporated into comets and asteroids before their delivery and detection on Earth such as in the Murchison meteorite.

Geochemical Sources and Availability of Amidophosphates on the Early Earth

Phosphorylation of (pre)biotically relevant molecules in aqueous medium has recently been demonstrated using water-soluble diamidophosphate (DAP). Questions arise relating to the prebiotic availability of DAP and other amidophosphosphorus species on the early earth. Herein, we demonstrate that DAP and other amino-derivatives of phosphates/phosphite are generated when Fe₃ P (proxy for mineral schreibersite), condensed phosphates, and reduced oxidation state phosphorus compounds, which could have been available on early earth, are exposed to aqueous ammonia solutions. DAP is shown to remain in aqueous solution under conditions where phosphate is precipitated out by divalent metals. These results show that nitrogenated analogues of phosphate and reduced phosphite species can be produced and remain in solution, overcoming the thermodynamic barrier for phosphorylation in water, increasing the possibility that abiotic phosphorylation reactions occurred in aqueous environments on early earth.

An interstellar synthesis of phosphorus oxoacids

Phosphorus signifies an essential element in molecular biology, yet given the limited solubility of phosphates on early Earth, alternative sources like meteoritic phosphides have been proposed to incorporate phosphorus into biomolecules under prebiotic terrestrial conditions. Here, we report on a previously overlooked source of prebiotic phosphorus from interstellar phosphine (PH3) that produces key phosphorus oxoacids-phosphoric acid (H3PO4), phosphonic acid (H3PO3), and pyrophosphoric acid (H4P2O7)-in interstellar analog ices exposed to ionizing radiation at temperatures as low as 5 K. Since the processed material of molecular clouds eventually enters circumstellar disks and is partially incorporated into planetesimals like proto Earth, an understanding of the facile synthesis of oxoacids is essential to untangle the origin of water-soluble prebiotic phosphorus compounds and how they might have been incorporated into organisms not only on Earth, but potentially in our universe as well.

Nitrogenous Derivatives of Phosphorus and the Origins of Life: Plausible Prebiotic Phosphorylating Agents in Water

Phosphorylation under plausible prebiotic conditions continues to be one of the defining issues for the role of phosphorus in the origins of life processes. In this review, we cover the reactions of alternative forms of phosphate, specifically the nitrogenous versions of phosphate (and other forms of reduced phosphorus species) from a prebiotic, synthetic organic and biochemistry perspective. The ease with which such amidophosphates or phosphoramidate derivatives phosphorylate a wide variety of substrates suggests that alternative forms of phosphate could have played a role in overcoming the "phosphorylation in water problem". We submit that serious consideration should be given to the search for primordial sources of nitrogenous versions of phosphate and other versions of phosphorus.