[M-IS07] Astrobiology

[MIS07-P05] Quantitative Understanding of Nucleoside Phosphorylation in Supercritical CO₂ / Water Two-Phase System

*Kohei Morino^1,2, Shotaro Tagawa^1,2, Shohei Terazawa^1,2, Kosuke Fujishima^1,3 (1.Earth-Life Science Institute (ELSI), Tokyo Institute of Technology, 2.School of Life Science and Technology, Tokyo Institute of Technology, 3.Graduate School of Media and Governance, Keio University)

Keywords:Astrobiology, Origin of life, Chemical evolution, Supercritical CO2

Nucleotides derived from nucleoside phosphorylation are one of the essential biomolecules for life and are thought to have played an important role in the origin of life. Previously nucleotide synthesis has been reported simulating the Earth's surface environments such as hot springs and Darwin's warm little pond. Nevertheless, it has been suggested that the ozone layer did not exist on the early Earth, and that the main components of the atmosphere, such as water vapor and CO₂, were insufficient to shield the ultraviolet rays that reach the surface, thus preventing the stable existence of building blocks for life. On the other hand, the deep-sea environment is isolated from such ultraviolet radiation. While the deep-sea environment is known to be water-rich and therefore dehydration reactions such as phosphorylation are considered thermodynamically unfavorable. However, in recent decades, a natural pool of liquid CO₂ has been discovered in the deep-sea. The mild critical point of CO₂ (Tc = 31.1 ℃ and Pc = 7.38 MPa) permits its existence as a hydrophobic solvent in its supercritical states near the deep-sea hydrothermal system.
Previously we have shown that supercritical CO₂ (scCO₂) - water two-phase system can drive nucleoside phosphorylation under conditions above 70 ℃ and 11-12 MPa. However, the precise reaction mechanism remains unsolved because of the lack of quantitative measurement of production yields at specific temperature, pressure, and duration. Therefore, we improved the experimental setup and performed series of quantitative experiments to measure the product yield under stable temperature and pressure. The result indicated that the new system was capable for reducing the standard deviation of temperature and pressure by half and the standard deviation of the product yield by 1/6 compared with the system in the previous study. Experiments were also conducted using this experimental setup to change the area of the two-phase interface, and it was found that the product yield increased with an increase in the interfacial area. These results suggest a new hypothesis that the reaction proceeds at the scCO₂/water interface of the two-phase system.
This quantitative approach could serve as a foundational steppingstone when studying reactions in two-phase systems of scCO₂ and water. Furthermore, by quantifying the experimental data, the reaction rate can be determined. Furthermore we expect that it will be possible to gain insight towards kinetic understanding, including the activation energy, both experimentally and computationally.