Mechanochemical milling experimentsAll milling experiments were conducted using InSolido Technologies vibratory ball mill and in 14 mL hardened stainless steel (SS) containers specifically designed for high temperature milling reactions. Three 1 g SS balls (6 mm in diameter) were used as milling media, reactions were conducted at 30 Hz frequency and all reactions were performed for the duration of 18h. ATR-FTIR & PXRDSpectra were recorded on PerkinElmer SpectrumTwo spectrometer equipped with a diamond cell in a 4000-400 cm -1 range. PXRD patterns were collected on PanAlytical Aeris diffractometer (Cu Kα radiation and Ni filter) and zero background sample holder. IP-HPLCOligopeptides were analyzed by IP-HPLC on an Agilent 1290 Infinity instrument equipped with a Phenomenex Luna C18 column (250 mm long, 4.6 mm diameter and 3 µm particle size). The mobile phase was an aqueous solution of 50 mM KH2PO4 and 7.2 mM sodium hexanesulfonate adjusted to pH 2.5 by the addition of 85% H3PO4 (HPLC grade). The mobile phase was used isocratically with 1 mL/min flow rate. Sample injection volume of 1 µL was used, the total method time was 20 min and the column was equilibrated at 30°C. The instrument was

The presence of amino acids on the prebiotic Earth, either stemming from endogenous chemical routes or delivered by meteorites, is consensually accepted. In contrast, prebiotically plausible pathways to achieve peptides from unactivated amino acids are still unclear since most oligomerization approaches rely on thermodynamically disfavored reactions in solution. Alternative hypotheses such as the prebiotic impact scenario postulate that the mechanical impacts from meteorites and geochemical phenomena played an important role in delivering exogenous material to Earth, thus providing the geochemical, mechanical, and thermal conditions to synthesize small prebiotic organic compounds in the absence of bulk liquid media. In this context, here we evaluate the applicability of mechanochemistry by ball milling for peptide bond formation under a prebiotic impact scenario. We found that the combination of mechanical forces and prebiotically plausible and ubiquitous minerals as activators enable the oligomerization of amino acids such as glycine in the absence of bulk water (or solvents) and at ambient temperature. Increasing the mechanochemical reactor's temperature is shown to favor the degree of polymerization concomitantly with the formation of cyclic glycine dimer [cyclo(Gly 2 ) or DKP], a product commonly considered as a dead-end in solution peptide bond formation. However, our study shows that DKP can be mechanochemically activated and used as a source for glycine oligomers. The findings of this research provide alternative mechanochemical routes towards oligopeptides and establish new synthetic approaches for prebiotic chemistry that are not limited by poor diffusion of the reactants, thus complementing the current alternating wetting and drying prebiotic environment strategy. File list (2) download file view on ChemRxiv Peptide paper.pdf (816.75 KiB) download file view on ChemRxiv Peptide paper-SI.pdf (1.79 MiB)

<p>The presence of amino acids on the prebiotic Earth, either stemming from endogenous chemical routes or delivered by meteorites, is consensually accepted. In contrast, prebiotically plausible pathways to achieve peptides from unactivated amino acids are still unclear since most oligomerization approaches rely on thermodynamically disfavored reactions in solution. Alternative hypotheses such as the prebiotic impact scenario postulate that the mechanical impacts from meteorites and geochemical phenomena played an important role in delivering exogenous material to Earth, thus providing the geochemical, mechanical, and thermal conditions to synthesize small prebiotic organic compounds in the absence of bulk liquid media. In this context, here we evaluate the applicability of mechanochemistry by ball milling for peptide bond formation under a prebiotic impact scenario. We found that the combination of mechanical forces and prebiotically plausible and ubiquitous minerals as activators enable the oligomerization of amino acids such as glycine in the absence of bulk water (or solvents) and at ambient temperature. Increasing the mechanochemical reactor’s temperature is shown to favor the degree of polymerization concomitantly with the formation of cyclic glycine dimer [cyclo(Gly₂) or DKP], a product commonly considered as a dead-end in solution peptide bond formation. However, our study shows that DKP can be mechanochemically activated and used as a source for glycine oligomers. The findings of this research provide alternative mechanochemical routes towards oligopeptides and establish new synthetic approaches for prebiotic chemistry that are not limited by poor diffusion of the reactants, thus complementing the current alternating wetting and drying prebiotic environment strategy.</p>

<p>The presence of amino acids on the prebiotic Earth, either stemming from endogenous chemical routes or delivered by meteorites, is consensually accepted. In contrast, prebiotically plausible pathways to achieve peptides from unactivated amino acids are still unclear since most oligomerization approaches rely on thermodynamically disfavored reactions in solution. Alternative hypotheses such as the prebiotic impact scenario postulate that the mechanical impacts from meteorites and geochemical phenomena played an important role in delivering exogenous material to Earth, thus providing the geochemical, mechanical, and thermal conditions to synthesize small prebiotic organic compounds in the absence of bulk liquid media. In this context, here we evaluate the applicability of mechanochemistry by ball milling for peptide bond formation under a prebiotic impact scenario. We found that the combination of mechanical forces and prebiotically plausible and ubiquitous minerals as activators enable the oligomerization of amino acids such as glycine in the absence of bulk water (or solvents) and at ambient temperature. Increasing the mechanochemical reactor’s temperature is shown to favor the degree of polymerization concomitantly with the formation of cyclic glycine dimer [cyclo(Gly₂) or DKP], a product commonly considered as a dead-end in solution peptide bond formation. However, our study shows that DKP can be mechanochemically activated and used as a source for glycine oligomers. The findings of this research provide alternative mechanochemical routes towards oligopeptides and establish new synthetic approaches for prebiotic chemistry that are not limited by poor diffusion of the reactants, thus complementing the current alternating wetting and drying prebiotic environment strategy.</p>