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

Abstract

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.

Prebiotic Syntheses of Organophosphorus Compounds from Reduced Source of Phosphorus in Non-Aqueous Solvents

“…Deionized water (DI, hereafter) was obtained in-house by using a Barnstead (Dubuque, IA, USA) NANO pure ® Diamond Analytical combined reverse osmosis-deionization system [39]. The semi-aqueous solvent UAFW was prepared as in prior studies by using a 1:2:4 molar ratio of urea: ammonium formate: water [30].…”

“…For 31 P-NMR analyses, the samples were analyzed on a 600-MHz Bruker Neo NMR operating at 242.9 MHz in both H-coupled and H-decoupled modes. The width of the spectrum was 200 ppm, and the running temperature was 22 • C. The P products of the reactions were quantified by peak integration method as previously reported [39,[48][49][50][51]. The relaxation time (D1) used between NMR scans throughout this study was set to 2 s. This was compared to several experiments run at D1 = 30 s. Since the integral values of D1 = 2 s and D1 = 30 experiments were comparable, a D1 = 2 s is considered quantitative, and the remaining experiments were run at D1 = 2 s. The sample preparation for the NMR analysis has been discussed in detail in Section 2.2.…”

“…These reduced P compounds also undergo a condensation reaction in the presence of urea and under mild heating conditions (i.e., heating to dryness), and form energetic condensed reduced P compounds, including pyrophosphite and the mixed-valence compounds isohypophosphate [39]. These high-energy condensed P compounds react with organics to form organophosphorus compounds [39].…”

“…The reduced P compounds oxidize into phosphate PO 4 3− (1) in the presence of ultraviolet light and H 2 S/HS − , via a thiophosphate intermediate [40], (2) by auto-oxidation under mild heating and in the presence of condensation agents [39], and (3) by oxidation with H 2 O 2 catalyzed by Fe 2+ [41], called the Fenton reaction. This Fenton reaction produces reactive •OH and •OOH radicals that oxidize reduced P compounds by cleaving the H-P bond to generate a phosphite radical.…”

Evolution of the substrate specificity of an RNA ligase ribozyme from phosphorimidazole- to triphosphate-activation

“…Therefore, kinetically more stable 5′-triphosphorylated building blocks would have been better substrates for RNA assembly if they were readily generated on the early Earth and suitable enzymes were available to use them. 5′-triphosphorylated RNA monomers and oligomers can be generated by reactions with abiotically synthesized polyphosphates, such as cyclic-trimetaphosphate (10)(11)(12) and ribozymes that accelerate this triphosphorylation reaction have been reported. (13,14) Additionally, triphosphate substrates may be produced by the reaction of phosphorimidazolides with pyrophosphate, the latter abundantly generated in mineral films in alkaline hydrothermal environments.…”