[BBC03-02] Pressure-induced esterification reaction between phosphoric acid and methanol: a possibility of prebiotic formation of alkyl phosphate and phospholipid at high pressure
Keywords:pressure-induced esterification, DAC, methyl phosphate, prebiotic evolution
A H3PO4-CH3OH-H2O mixture (molar ratio H3PO4:CH3OH:H2O =1:5:4) was loaded in an encapsulating gasket and high pressure was applied using a Paris-Edinburgh press. The sample was kept at 6 GPa for 3 days at room temperature. Then, the sample was recovered to ambient pressure and analyzed using LC-MS. The obtained mass chromatograms clarified the formation of monomethyl phosphate and dimethyl phosphate with the yields of 13% and 0.5%, respectively, which were much higher than the yields at ambient pressure (0.5% for monomethyl phosphate and 0 for dimethyl phosphate). The result proved that the high pressure promoted the esterification reaction.
To look into the mechanism of the pressure-induced reaction, we conducted in situ observations on the H3PO4-CH3OH-H2O mixture at high pressure using diamond anvil cells (DAC) with a culet diameter of 600 µm. Samples were loaded into metal gasket holes with the diameters of 200-300 µm, and the pressure was estimated using the ruby fluorescence pressure scale2. After increasing the pressure, we observed crystallization of the mixture at 4.3 GPa. From the X-ray diffraction pattern and Raman spectra, we confirmed the existence of ice VII. It suggests that the crystallization of water is likely to be the driving force of this reaction.
1. Drabek-Maunder E et al. (2019), International Journal of Astrobiology, 18(1), 25-32.
2. Mao HK et al. (1986), Journal of Geophysical Research: Solid Earth, 91, 4673-4676.