Meteorite‐Assisted Phosphorylation of Adenosine Under Proton Irradiation Conditions

The abiotic phosphorylation of nucleosides is a major hurdle in origin-of-life studies. We suggest a plausible pathway for the synthesis of adenosine nucleotides from adenosine and NaH2PO4 under radiative conditions mimicking the solar wind in the presence of a meteorite of the aubrite-type. Hydroxyapatite also performed as a mineral heterogeneous phosphorus source. Adenosine polyphosphate derivatives and inorganic polyphosphates were detected in the reaction mixture, highlighting the high reactivity of the system. Both the total yield of adenosine nucleotides and the conversion of adenosine increased upon performing the irradiation in the presence of formamide (NH2CHO) and aubrite. These experiments simulate conditions in space or on an early Earth fluxed by protons from the solar wind, potentially mimicking a plausible prebiotic phosphorylation scenario.


Introduction
Phosphorylation is fundamental for cellular growth and survival. It controls metabolic pathways, as well as the structural organization of the cell and provides reactivity . [1] The biosynthesis of nucleotides and polyphosphates is performed in extant systems by several kinases evolved to reach this goal. The intermediate steps between prebiotic and extant biological worlds have been recently discussed. [2] Pre-biological conditions bona fide entailed simpler reagents and chemical conditions. [3] In this context, the attention has been focused on aqueous scenarios under thermal conditions (range of temperature from 333 K to 373 K), [4] using different phosphorus sources, such as orthophosphate [4][5][6] condensed phosphates, [7] mineral phosphates, [8] and reduced phosphorus(III) reagents. [9] These conditions usually required the presence of condensing agents and/or catalysts to overcome the unfavorable thermodynamic balance of the process. [10,11] Analysis and review of the role of condensing agents and catalysts in abiotic phosphorylation reactions, [12] such as the role of urea in phosphorylation reactions, are reported in the literature. [13] Phosphorylation using hydroxyapatite as source of phosphate was observed in the presence of formamide under thermal conditions. [14] The fact that urea and formamide act as organic catalysts in some of these processes does not detract from the observation that mineral catalysts could have had an important role, as actually shown in this study and in other previous studies on the syntheses of nucleic acids precursors. [14,15] Mixtures of positional isomers (acyclic monophosphates and cyclic monophosphates), associated to degradation products, were observed in different amounts depending on the experimental conditions. Early studies on the condensation of water-soluble phosphates to polyphosphates and on the phosphorylation, condensation, or polymerization of biomolecules with polyphosphates have been reviewed. [16,17] Solvents alternative to water, such as deep eutectic [18][19][20] and formamide (NH 2 CHO), [21,22] have been also used, meeting different degrees of success, NH 2 CHO being able to contemporaneously solubilize nucleosides, reagents and active phosphorus species. [23] NH 2 CHO is among the plausible chemical precursors for the prebiotic synthesis of nucleic acids (for the prebiotic relevance of NH 2 CHO see SI# 1). [24,25] It has been detected in dense diffuse interstellar clouds, in the galactic habitable zone, in comets and in satellites. [26,27] Despite the large attention devoted to thermal processes, the data available on the role that other forms of energy present on the primitive Earth (and in space-wise conditions) might have played in the phosphorylation of nucleosides are scarce. As an example, adenosine was phosphorylated in dry-film conditions at room temperature using vacuum ultraviolet (VUV) radiation or γ-radiation, in the presence of sodium orthophosphate (NaH 2 PO 4 ) or of more complex phosphorus minerals. [28] Recently, we reported that a high-energy proton beam, modelling the solar wind, can be successfully used for the synthesis of variegate and prebiotically relevant panels of compounds, including four of the natural nucleosides, formed from NH 2 CHO in the presence of meteorites (iron, stony iron, chondrite, and achondrite types). [29] In addition, the complete panel of nucleobases in RNA and DNA molecules is synthesized from NH 2 CHO and meteorites in high-energy-density events modeling the extraterrestrial impact of the meteorite on the surface of the primitive Earth. [30] May high energy protons, meteorites and NH 2 CHO mediate the phosphorylation of nucleosides? Pioneering studies described that the phosphorylation of adenosine in solid dry-film condition under low energy proton irradiation (6.75 MeV) can occur using NaH 2 PO 4 as a phosphorus source. [31] NaH 2 PO 4 has been selected on the basis of the reported phosphate reactivity: NaH 2 PO 4 > Na 2 HPO 4 @ Na 3 PO 4 . [32] In this latter case, a mixture of acyclic and cyclic nucleotide mono-phosphate isomers was obtained in low total yield relative to the converted substrate. A decrease in the total yield of nucleotides was observed increasing the energy of the proton beam. Similar results were obtained in the exposure of a dry film of 2'-deoxy adenosine and NaH 2 PO 4 in real space experiments performed on a satellite. [33] Here we report that adenosine is efficiently phosphorylated by NaH 2 PO 4 in dry film conditions under high-energy proton irradiation (170 MeV) in the presence of the aubrite meteorite NWA 2828, affording the corresponding nucleotides in high total yield and conversion of substrate. Hydroxyapatite also performed as heterogeneous phosphorus source. Both yield and conversion were further increased performing the irradiation in the presence of NH 2 CHO. Adenosine polyphosphate derivatives ApNs (from adenosine diphosphate ADP to adenosine tridecaphosphate Ap13) and inorganic polyphosphates PNs (from P3 to P14) were also detected in the reaction mixture, highlighting the high reactivity of the system. The reaction pathway of the phosphorylation process has been tentatively interpreted on the basis of computational studies focusing on the possible role of NH 2 CHO and of the sugar residue in adenosine.

Phosphorylation of Adenosine
The phosphorylation of adenosine 1 was performed in four experimental conditions: A) adenosine and NaH 2 PO 4 in dry-film condition; B) adenosine, NaH 2 PO 4 and NWA 2828 powder in dry-film condition; C) adenosine and NaH 2 PO 4 in NH 2 CHO suspension; and D) adenosine, NaH 2 PO4 and NWA 2828 powder in NH 2 CHO suspension. NWA 2828 is an achondrite of the aubrite type meteorite. At least 65 different achondrite meteorites have been classified prior to 2015 as members of the aubrite type, including the Allan Hills, LaPaz Icefield, Lewis Cliff, Miller Range, Elephant Moraine and Northwest Africa groups. Examples of comprehensive Reviews are reported in Ref. [34][35][36]. Aubrites derive from asteroids of the E-type [mainly of the E(II) sub-class)], such as the asteroid 2867 Steins, that was the target of the Rosetta mission. [37] The aubrites are considered as a fascinating group of meteorites because they represent, in many of their properties, the end members in the spectrum of conditions of formation of igneous meteorites from asteroids. They formed very early in the history of the solar system, being suggested as geochemical markers for highspeed ejection processes occurring on Mercury, Mars and the pristine Earth. [38,39] The prebiotic interest of NWA2828, the reasons for having chosen it in this study, its cosmologic origin and mineralogical characterization are reported in SI# 2. [40] NWA 2828 contains schreibersite [(Fe, Ni) 3 P], a mineral that was studied in the thermal phosphorylation of nucleosides under radical conditions . [41] Solid films were prepared by air drying of aqueous mixtures (300 μL) of adenosine (0.4 mmol) and NaH 2 PO 4 (50 mg, 0.4 mmol) in the presence or absence of NWA 2828 powder (2.0 mg). As an alternative, hydroxyapatite (50 mg) was used as phosphorus source. When required, the irradiation was performed in the presence of NH 2 CHO (200 μL) under similar experimental conditions. The samples were irradiated at 298 K with 170 MeV protons for 3 min at the Phasatron accelerator facility of the Joint Institute of Nuclear Research of Dubna (Moscow region, Russia). The uniform proton field was bounded to 10 × 10 cm 2 by the collimator system. The averaged linear energy transfer (LET) was 0.57 keV/μm and the calculated absorbed dose was 6.0 Gy. The solar wind was discovered and measured by the Mechta probe and by the Mariner 2 spacecraft, [42] and it consists of protons and electrons. The proton irradiation conditions used in this study (170 MeV; dose, 6 Gy) are in the same range of intensity of the solar wind and are of the same order of magnitude as that actually experienced during the phosphorylation of nucleosides in space flight conditions. [33,43] These conditions were used in groundbased experiments to model chemical transformations on asteroids. [44] The presence of organics in the original sample of NWA 2828, usually observed in the very low ppb range, [45] was prevented as reported. [46] We focused on the detection of nucleotides by reverse-phase ultra-high performance liquid chromatography associated with mass-spectrometry (UHPLC-MS). The structure of products was unambiguously assigned by comparison of the retention time and characteristic mass fragmentation peaks with original commercial samples. The description of the UHPLC-MS procedure, and the UHPLC analyses of adenosine 1, adenosine nucleotides 2-7, and adenine 8, are reported in SI #3 The formation of acyclic and cyclic adenosine nucleotides was observed : irrespective to experimental conditions, the irradiation of adenosine 1 and NaH 2 PO 4 afforded 5'-adenosine mono-phosphate (5'-AMP) 2, 3'-adenosine mono-phosphate (3'-AMP) 3, 2'-adenosine mono-phosphate (2'-AMP) 4, and 2',3'cycloadenosine monophosphate (2',3'-cAMP) 5, in addition to adenine 8, formed as a consequence of the partial breaking of the β-glycosidic bond (Scheme 1, Figure 1). In addition, 3',5'cycloadenosine monophosphate (3',5'-cAMP) 6, and 5'-adenosine diphosphate (5'-ADP) 7, were obtained in reaction B, and reactions B and D, respectively (Scheme 1, Figure 1). The retention time (min) and the specific m/z values corresponding to the targeted molecules are reported in Table 1 (m/z fragmentation spectra of compounds 1-8, and the current ion profile and ESI(+)/MS/MS spectra of reaction D, as selected example, are in SI #3). The very fact that adenosine nucleotides were observed at the end of the irradiation indicates that the overall balance of the synthesis/degradation process is positive.
The yield of nucleotides and the conversion of adenosine are reported in Table 2. Data on the irradiation of adenosine (1.3 mmol) and NaH 2 PO 4 (1.3 mmol) at 243 K in dry-film condition with slow 6.0 MeV protons are also indicated in Table 2 as a reference (reaction E). As a general trend, the total yield of nucleotides in dry-film condition was significantly higher with NWA 2828 ( Table 2, reaction B) than in the presence of adenosine and NaH 2 PO 4 alone, under both high-energy ( Table 2, reaction A) and low-energy ( Table 2, reaction E) proton beam irradiations. A similar trend was observed performing the irradiation in NH 2 CHO ( Table 2, reaction C versus reaction A and reaction E), suggesting a beneficial role of NWA 2828 and NH 2 CHO in the efficacy of the phosphorylation process. This hypothesis was further confirmed by reaction D, in which the contemporaneous presence of both NWA 2828 and NH 2 CHO afforded the highest total yield of adenosine nucleotides and the highest conversion of substrate (Table 2). In this latter case, the total yield of nucleotides was comparable, or higher, than that previously obtained by thermal phosphorylation of adenosine with orthophosphate in NH 2 CHO at either 310 K for several months, 343 K for 15 days, [18] and 363 K for 12 days [14] respectively. Irrespective of the physical state of the system (that is dry-film versus NH 2 CHO), lower amounts of adenine were detected in the presence of NWA 2828, indicating a possible role of the mineral in stabilizing the β-glycosidic bond during the phosphorylation process ( Table 2, reactions B and D). [49] NH 2 CHO alone does not exert the same effect (reaction C). The stabilization of the β-glycosidic bond in the presence of meteorites during irradiation experiments has been previously observed in the prebiotic synthesis of adenosine and 2'deoxyadenosine from adenine and sugars, as a possible result of surface interaction effects. [50] The decisive catalytic role of meteorites in NH 2 CHO prebiotic synthesis of nucleic acids has been recently reviewed. [51] NWA 2828 and NH 2 CHO showed a slightly different regioselectivity in the phosphorylation of adenosine. While 2',3'-cAMP prevailed in the absence of NH 2 CHO (reactions A and B), 5'-AMP becomes the major reaction product in the presence of NH 2 CHO (reaction C).
This trend was further confirmed when the irradiation was performed in the mixture of NH 2 CHO with NWA 2828 (reaction D). The prevalence of 5'-AMP is usually observed during the thermal phosphorylation of adenosine with orthophosphate in NH 2 CHO. [19] As for the other nucleotide isomers, 2'-AMP was detected in yield higher than 3'-AMP, while 3',5'-cAMP was significantly synthesized only in reaction D.
The reactions AÀ D have been repeated in the described experimental conditions in the presence of hydroxyapatite as [a] The UHPLC analysis was performed by using a C18 column associated with mass spectrometer Q-Exactive (Thermo) in the positive mode (details are in the Supporting Information #3). an alternative mineral source of phosphorus ( Figure 2). In these latter cases, the formation of nucleotides was observed only in the presence of NH 2 CHO (Table 2). These results are in accordance with the key role played by NH 2 CHO in the solubilizing effect of phosphate from hydroxyapatite, as previously reported by us during thermal phosphorylation processes. [14] The reactions CÀ D in the presence of hydroxyapatite afforded nucleotides in a total yield lower than that obtained using NaH 2 PO 4 , probably due to the partial release of active phosphorus from the mineral ( Table 2). The 5'-ADP was not detected in the reaction mixtures. A slightly higher yield for nucleotides was observed in the presence of NWA 2828 with respect to NH 2 CHO alone ( Table 2, entry 6 versus entry 5). About the regio-selectivity of the reaction, hydroxyapatite showed a selectivity trend similar to NaH 2 PO 4, 3',5'-cAMP 6 being obtained only in the presence of NWA 2828 (reaction D)

Synthesis of Adenosine Polyphosphates and Inorganic Polyphosphates
The MALDI-TOF analysis of reactions AÀ D with NaH 2 PO 4 showed, in addiction to nucleotides 2-7, the presence of molecular ions corresponding to adenosine polyphosphates (ApNs), including adenosine triphosphate (ATP), adenosine pentaphosphate (Ap5), adenosine heptaphosphate (Ap7), adenosine nonaphosphate (Ap9), adenosine undecaphosphate (Ap11), and adenosine tridecaposphate (Ap13) ( Table 3). The MALDI-TOF analyses of reactions AÀ D, and of nucleotides 2-7, are in SI# 5. As reported in Table 3, ApNs bearing an odd number of phosphates were selectively obtained, suggesting the occurrence of the prevalent transfer of a pyrophosphate moiety to newly synthesized monophosphate derivative. This reaction pattern is of particular interest, since it is chemiomimetic of the extant mechanism of phosphorylation of purine nucleosides by the purine nucleotide pyrophosphotranferases (PNPs), a large family of enzymes which catalyzes the selective transfer of the pyrophosphate moiety from ATP to purine nucleotide monophosphates . [52] In addition to ApNs, the molecular ions of inorganic polyphosphates (PNs) from P3 up to P14 were also detected by the MALDI-TOF analysis in reactions BÀ D, the irradiation of adenosine and NaH 2 PO 4 in NH 2 CHO (reaction B) affording the largest panel of these products. PNs were not produced in reaction A ( Table 2). The irradiation of NaH 2 PO 4 alone in the presence of formamide (reaction F), and in alternative, in formamide/NWA 2828 mixture (reaction G) was also performed, confirming that polyphosphates were easily produced from NaH 2 PO 4 under the reported experimental conditions (Table 4, MALDI-TOF analyses of reactions FÀ G are in SI# 5). PNs are generally deemed to be key agents in prebiotic evolution having several phosphate residues linked by highenergy phosphorus-anhydride bonds as in ATP and ADP. [53] These polymeric compounds are usually produced by dehydration of orthophosphate at elevated temperatures, and have been synthesized in high yield in plausible prebiotic scenarios, such as volcanic condensates [17] and deep oceanic steam vents. [54] Urea can improve the yield of PNs from NaH 2 PO 4 by formation of carbamylphosphate and phosphoramidate intermediates. [4] This effect can be in principle played by NH 2 CHO, which has a similar nucleophilic amide moiety available for the interaction with electron-positive phosphate atoms. PNs are also produced from NaH 2 PO 4 by radical path-  www.chemsystemschem.org ways including both phosphorous and oxygen centered freeradical species, spontaneously produced by dissolution in buffered media of the meteoritic mineral Schreibersite (Fe,Ni) 3 P. [55] This latter reaction pathway is fully compatible with our irradiation conditions, during which radical species are expected to be produced as a primary effect of ionizing radiation.

Reaction Pathway for the Formation of Polyphosphates
Proton-irradiation-induced formation of PNs observed in our experiments can be rationalized considering a reductive chemistry due to the remarkable amount of atomic H formed from phosphate or formamide under radiolysis conditions. [56][57][58] Our computations suggest that orthophosphates may readily bind atomic hydrogen yielding the Pcentered * P(OH) 4 radicals with a relatively low activation energy of + 11.3 kcal/mol in an exothermic chemistry that is accompanied with a reaction free energy change (hereafter abbreviated as ΔG r ) of À 10.4 kcal/mol (see the computed free energy profile in Figure 3). Subsequent dimerization of two * P(OH) 4 radicals yields a PÀ P bonded intermediate, having two equivalent phosphorus atoms in the + 4 formal oxidation state. After pseudo-rotation and a subsequent internal proton transfer, this intermediate dissociates to phosphoric acid (H 3 PO 4 ), phosphorous acid (H 3 PO 3 ) and water in a practically barrierless process in a markedly exergonic chemistry with a ΔG r of À 47.2 kcal/mol. Note, that the formation of phosphorous acid has also been observed in other radical-assisted phosphorylation reactions conducted using the meteoritic mineral schreibersite. [59] Phosphorous acid, similarly to phosphoric acid, may lose an atomic H leading to a P-centered H 2 PO 3 radical, as shown in Scheme 2, in an exergonic chemistry (computed ΔG r = À 27.3 kcal/mol). This radical may then spontaneously recombine with an Ocentered H 2 PO 4 radical (the latter prevalently forms upon radiolysis of phosphoric acid or its H-containing salts [56,57] yielding pyrophosphates (Scheme 2).

Reaction Pathway for the Formation of Adenosine Nucleotides
PNs are most probably involved in the phosphorylation of adenosine and in the formation of the ApNs that we observed in the irradiation experiments. In this context, several studies on the phosphorylation and polymerization of nucleosides and other biomolecules by use of PNs as reagents [60] were performed. In accordance with this hypothesis, the formation of ApNs from AMP by treatment with PNs in buffered NH 4 Cl solutions of bivalent metal ions has been reported to occur after 16 days at 310 K. In this reaction, the bivalent metal ions were able to coordinate two oxygen atoms of the PNs phosphate chain, favoring the hydrolysis of the anhydride bonds to yield trimetaphosphate, suggested as the actual phosphorylating agent. [61] Under these experimental conditions, the Ap3 derivative, corresponding to the transfer of the pyrophosphate moiety to starting AMP, was detected as the main component of the reaction mixture. Moreover, the possible transfer of the pyrophosphate moiety from in situ generated ATP to adenosine cannot be completely ruled out.
As an alternative, the possibility of a phosphorylation mechanism of adenosine based on a radicaI pathway has been evaluated. Indeed, early studies suggest that the main reaction channel of the radiolysis of aqueous NaH 2 PO 4 solutions involves the reaction of H 2 PO 4 À ions with hydrated electrons leading to HPO 4 * À radical anion and the release of an atomic H. [62,63] Reference 59 reports that atomic H is abundantly formed upon the radiolysis of formamide as well. Thus, similar to reference [61] a reductive chemistry associated with the presence of atomic H in the reaction mixture may feature a possible radiationinduced phosphorylation mechanism in our experiments. Thermodynamic driving force for the phosphorylation reaction with phosphate radicals is enormous, because the process is fueled by a highly exergonic radical recombination step between the phosphate radical and H * . For example, the computed free energy change balance for the reaction H 2 PO 4 * + adenosine + H * = 3'-AMP + H 2 O is À 104.6 kcal/mol, which is far better than that of the reaction between adenosine and pyrophosphates. [62] Note that radical assisted-reactions generally proceed on a much higher energy scale than that of common biochemical reactions. [63] Radiolysis of polyols, like ribose, is known to proceed via H-abstraction from one of the CÀ H bonds, [64] yielding the C-centered radical I (Scheme 3) or other isomers, differing in the position of the radical center. In the next reaction step radical I recombines with an HPO 4 * À radical ion yielding II. In this latter case the addition of HPO 4 À is expected to occur from the alpha-side of the carbonyl moiety in accordance with data previously reported. [65] Compound II is a hemiacetalic-type compound and thus it is prone to undergo a proton-assisted S N 1-type water loss leading to the carbocationic intermediate III. Note that proton-irradiation tracks are known to concentrate H + ions accessible for acid catalysis: analogous S N 1-type degradation of acetals upon proton-irradiation is well-known. [66] Theoretical calculations on a simplified Scheme 3. Phosphorylation mechanism of adenosine based on a radicaI pathway. Transiently formed metaphosphoric acid (HPO 3 ) may act as a phosphorylating agent. model (for details see the Supporting information SI#6) showed that III (Figure 4) is mainly stabilized by electrostatic interactions: i. e. it rather corresponds to the resonance structure in which the oxidized keto-ribose derivative is electrostatically bound to the partially positively charged phosphorus of a metaphosphoric acid unit. This suggests that intermediate III is prone to lose a metaphosphoric acid, which is a potent phosphorylating agent. Let us note that albeit metaphosphoric acid is obviously not stable in an aqueous environment, our state-of-the-art quantum molecular dynamics simulations (detailed in the Supporting Information) highlight that it may be stabilized in formamide via binding the oxygen of formamide to the phosphorus of metaphosphoric acid. Transiently formed metaphosphoric acid may survive in dry material as well. This hypothesis is in accordance with the detection of the m/z = 266 peak corresponding to the [M + 1] signal of intermediate IV in the MALDI-TOF analysis of reaction D (SI# 5).

Conclusions
We have described the formation of phosphorylated compounds from the nucleoside adenosine in the presence of a simple phosphorus source. The reaction is activated by a proton beam, is stimulated by formamide and by aubrite powder.
When tested together, formamide and aubrite further enhance the reaction and widen the panel of the formed compounds. To the best of our knowledge, nucleotides have never been detected in meteorites, [26][27][28] which is possibly due to the known low stability of these compounds. The purpose of testing the possibility of phosphorylating nucleosides using proton irradiation as energy source is three-fold. In the first place this radiation is used for its practical potential of inducing radicals, thus allowing reactions based on radical chemistry. The interest of this approach is general, given that radicals can be induced in many other possible ways. The second interest is that solar radiation was most likely a source of some degree of available energy on early Earth, independent on the evolution of geomagnetism. How strong was the protection effect by geomagnetism in Hadean and Paleoarchean times is still matter of debate, because of the difficulty of establishing a precise time frame for the Hadean geodynamo. [67,68] In the third place, the induction of phosphorylation by a mimic of a solar wind has interest per se, and its results may apply to any celestial body receiving irradiation from its star, not limiting to our local and particular radiation production-and-protection system. The phosphorylation occurs at every possible position of the sugar moiety, affords acyclic and cyclic compounds (both mono-and poly-phosphorylated, from adenosine diphosphate ADP up to adenosine tridecaphosphate Ap13) and is accompanied by the formation of inorganic polyphosphates PNs (from P3 to P14), highlighting the high reactivity of the system. The fact that adenosine nucleotide polyphosphates (ApNs) form following an odd-values numerical series indicates that the elongation of the polyphosphate chain likely occurs by addition of pyrophosphate units to a starting monomer, anticipating the extant biological reactions carried out by purine nucleotide pyrophosphotranferases. The various alternatives of the pathways involved are discussed and are all compatible with the observed stimulatory action of formamide and the aubrite. Interestingly, the radical pathway described for the formation of AMP entails the formation of metaphosphoric acid as possible phosphorylating agent. Quantum molecular dynamics simulations suggest that metaphosphoric acid may be stabilized by formamide. The relative promptness, the high yield and the regioselectivity of the phosphorylation products point to the possible prebiotic relevance of the scenario depicted here, which involves proton beams, aubrite and the one-carbon atom compound formamide. Thus, nucleotides may form in the same physicalchemical frame in which the formation of nucleic bases and of nucleosides has been reported. [25] Unfortunately, the drastic conditions normally used for the analysis of the organic content of meteorites are expected to destroy low-stable organics, such as nucleosides and nucleotides.
This working model might have happened on a planet like Earth in the presence of falling meteorites. The biomimetic nature of the poly-phosphorylation reaction adds to this plausibility. The relevance of proton irradiation as a source of energy for radical chemistry is universal, and should not be dismissed focusing only on the precise geo-evolution of this planet.

Preparation of Aubrite Powder
Dust samples of NW2828 (approximately 100 mg) were extracted by a two-steps procedure to remove organics. The first consisted in the addition of 1.0 mL 0.1 N NaOH and 3.0 mL of 2 : 1 chloroformmethanol, the second step in the addition of 1.0 mL 0.1 N sulfuric acid and 3.0 mL of 2 : 1 chloroform-methanol. Between steps the powder was recovered by centrifugation (6000 rpm, 10 min) and the supernatant phase was decanted. The supernatant contained organics that were soluble in both aqueous and organic solvents at high and low pH ranges, leaving behind the powder of the meteorite. Finally, the powder was pyrolyzed at 600°C to remove the insoluble organic component in the laboratory oven for 1 h.

Irradiation Experiments
General procedure: Solid films were prepared by air drying of aqueous mixtures (300 μL) of adenosine (0.4 mmol) and NaH 2 PO 4 (50 mg, 0.4 mmol) or hydroxyapatite (50 mg) in the presence or absence of NWA 2828 powder (2.0 mg). When required, the irradiation was performed in NH 2 CHO (200 μL) under similar experimental conditions. The samples were irradiated at 298 K with 170 MeV protons for 3 min. The uniform proton field was bounded to 10x10 cm 2 by the collimator system. The averaged linear energy transfer (LET) was 0.57 keV/μm and the calculated absorbed dose was 6.0 Gy. generated by the Phasotron facility of the Joint International Nuclear Institute (JINR; Dubna, Russia).

Quantum Chemical Calculations
Computations were carried out at DFT-level of theory using the 6-311 + + G** basis set of atomic orbitals and Becke's three parameters hybrid functional, [66] in combination with Lee-Yang-Parr's correlation functional. 70À 71 Free energy data were derived from frequency calculations performed at 298 K in harmonic approximation. Note that in the past the methodology has been benchmarked against CCSD(T) calculations, [72] and has successfully been used to describe the mechanism of several other radicalbased prebiotic reactions. [73] All computations were carried out in gas-phase using the Gaussian09 program package. [74] Further methodological details and comparison with general aspects of other frequently used computational approaches (e. g. metadynamics) [75][76] are addressed in the Supporting Information (SI# 6).