[BBC03-02] Pressure-induced esterification reaction between phosphoric acid and methanol: a possibility of prebiotic formation of alkyl phosphate and phospholipid at high pressure
キーワード：圧力誘起エステル化、ダイヤモンドアンビルセル、リン酸メチル、分子進化
Esterification reaction between phosphoric acid and alcohols is a possible origin of biomolecules with phosphoester bond, such as alkyl phosphate and phospholipid. Especially, studying the prebiotic formation of phospholipid becomes an important task in the discovery of the origin of life because phospholipid acts as a major component of cell membranes. Recently, the existence of organic materials, such as methanol, on ice bodies has been reported1. The interiors of ice planets and satellites at high pressure could be places for the prebiotic evolution of biomolecules, since the yield and reaction rate of some organic reactions increase dramatically under high pressure conditions. In this study, we investigated the pressure-induced esterification reaction between phosphoric acid and methanol, and proposed a possibility of the prebiotic formation of phospholipids at high pressure.
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.
References
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.
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.
References
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.