Phosphites as a source of Organophosphates on Prebiotic Earth

Phosphorus is an essential element for life and is present predominantly as phosphate in biological molecules such as phospholipids and nucleic acids. Phosphate minerals, such as hydroxyapatite, are the most abundant phosphorus-bearing rocks in the geological record from the early Earth. However, phosphates require large amounts of energy to react in water and are highly insoluble. The mechanism of phosphate incorporation into life on the early Earth is an active area of research and is commonly referred to as “the phosphate problem”. In contrast, phosphites have phosphorus in a lower oxidation state, are more reactive, and are more soluble in water than phosphates. Our hypothesis is that metal phosphites may have been the source of organophosphates (i.e., organic molecules that contain a phosphate group) on the early Earth. If our hypothesis is true, metal phosphites must then be able to phosphorylate organic molecules under prebiotically plausible conditions. In order to test our hypothesis, we reacted metal phosphites with glycerol in slightly acidic, aqueous conditions while heating at 60-75oC to mimic the prebiotic Earth. Resulting products have been identified through phosphorous, carbon, and hydrogen nuclear magnetic resonance (NMR) spectroscopy. After confirming successful phosphonylation, the resulting organophosphites were oxidized to organophosphates via Fenton chemistry and ultraviolet (UV) radiation in the presence of Fe2+. Preliminary results have shown that organophosphates do form in this two-step process and suggest that the cation paired with each phosphite influences the product yields. Currently, our experimental conditions are being optimized and experiments to determine quantitative product yields are being performed.