Presentation Information
[PPS12-07]Mineral-catalyzed Oligomer Formation under Simulated Europa Seafloor Conditions
*Chihaya Yamamoto1, Ayako Shinozaki2, Koichi Mimura1 (1.Graduate School of Environmental Studies, Nagoya University, 2.Faculty of Science, Hokkaido University)
Keywords:
Europa,Oligomerization,Mineral catalysis,High-pressure experiments
Europa is thought to possess a subsurface ocean approximately 100 km deep beneath its thick icy shell, and its seafloor, composed of serpentinized rocks, is estimated to be subjected to hydrostatic pressures of ∼150 MPa (e.g. Khurana et al. 1998; Vance et al., 2007; Marion et al., 2005). In addition, the delivery of organic compounds by comets and meteorites, as well as the possible presence of hydrothermal systems analogous to those in Earth's deep oceans, have been suggested (e.g. Pierazzo and Chyba, 2001; Teece et al., 2025). Through such hydrothermal activity and mineral catalytic effects, Europa's seafloor may provide an environment where organic polymerization and, ultimately, chemical evolution can be promoted (e.g. Corliss et al., 1981; Sousa et al., 2013). On the other hand, high-pressure and aqueous conditions inhibit dehydration-condensation reactions (Shock, 1992), and it remains unclear how these promoting and inhibiting factors interact in combination with respect to chemical evolution on Europa's seafloor. Therefore, it is necessary to evaluate the potential for chemical evolution by conducting laboratory simulation experiments to examine whether the polymerization of organic materials can proceed under the combined effects of temperature, mineral catalysis, and pressure.
In this study, we investigated the abiotic oligomerization of L-alanine under conditions simulating Europa's seafloor. The starting material consisted of a mixture of 6 mg aqueous solution containing several salts which are MgSO4 (60 mM), Na2SO4 (20 mM), and NaCl (15 mM) and L-α-alanine (100 mM), and 120 mg serpentinite powder, each prepared based on estimated oceanic and rock compositions of Europa (Zolotov and Shock, 2001; Thompson et al., 2021). The starting materials were sealed in PTFE double capsules and maintained at 150 MPa using a piston-cylinder apparatus at 5, 50, and 125℃ for 2, 4, and 10 days, respectively. After the experiment, the products and residual alanine were quantified using LC-MS/MS with an internal standard method.
As a result, despite the inhibitory effect of high pressure, the mineral surfaces constituting serpentinite promoted the formation of chain oligomers such as alanyl-alanine and trialanine, as well as the cyclic oligomer 2,5-diketopiperazine. Temperature affected both the formation efficiency and stability of the oligomers. At low to moderate temperatures (5℃ and 50℃), chain oligomers were dominant and remained stable. In particular, at 50℃, alanyl-alanine and trialanine were continuously formed throughout the experiment, whereas cyclization to 2,5-diketopiperazine was only observed on tenth day, and the yield was lower than that of alanyl-alanine. These results suggest that at the low to moderate temperature conditions, chain formation and elongation was promoted while intramolecular cyclization via dehydration was suppressed. On the other hand, at the high temperature condition (125℃), the formation of 2,5-diketopiperazine was favored over alanyl-alanine throughout the experiments. The yields of both oligomers versus experimental time at 125℃ showed a similar trend, characterized by rapid formation up to second day followed by rapid decomposition. This behavior indicates a dynamic balance between rapid oligomer synthesis and thermal degradation under high-temperature conditions.
These results suggest that high production efficiency and long-term stability of oligomers cannot be simultaneously achieved under a single temperature regime. Nevertheless, hydrothermal convection associated with temperature gradients may enable a cycle in which oligomers formed in high-temperature regions are transported to lower-temperature regions and preserved. This study suggests that mineral-catalyzed oligomerization can occur on Europa's seafloor, and that the combination of temperature gradients and water-rock interactions may enable further abiotic polymerization of organic molecules.
In this study, we investigated the abiotic oligomerization of L-alanine under conditions simulating Europa's seafloor. The starting material consisted of a mixture of 6 mg aqueous solution containing several salts which are MgSO4 (60 mM), Na2SO4 (20 mM), and NaCl (15 mM) and L-α-alanine (100 mM), and 120 mg serpentinite powder, each prepared based on estimated oceanic and rock compositions of Europa (Zolotov and Shock, 2001; Thompson et al., 2021). The starting materials were sealed in PTFE double capsules and maintained at 150 MPa using a piston-cylinder apparatus at 5, 50, and 125℃ for 2, 4, and 10 days, respectively. After the experiment, the products and residual alanine were quantified using LC-MS/MS with an internal standard method.
As a result, despite the inhibitory effect of high pressure, the mineral surfaces constituting serpentinite promoted the formation of chain oligomers such as alanyl-alanine and trialanine, as well as the cyclic oligomer 2,5-diketopiperazine. Temperature affected both the formation efficiency and stability of the oligomers. At low to moderate temperatures (5℃ and 50℃), chain oligomers were dominant and remained stable. In particular, at 50℃, alanyl-alanine and trialanine were continuously formed throughout the experiment, whereas cyclization to 2,5-diketopiperazine was only observed on tenth day, and the yield was lower than that of alanyl-alanine. These results suggest that at the low to moderate temperature conditions, chain formation and elongation was promoted while intramolecular cyclization via dehydration was suppressed. On the other hand, at the high temperature condition (125℃), the formation of 2,5-diketopiperazine was favored over alanyl-alanine throughout the experiments. The yields of both oligomers versus experimental time at 125℃ showed a similar trend, characterized by rapid formation up to second day followed by rapid decomposition. This behavior indicates a dynamic balance between rapid oligomer synthesis and thermal degradation under high-temperature conditions.
These results suggest that high production efficiency and long-term stability of oligomers cannot be simultaneously achieved under a single temperature regime. Nevertheless, hydrothermal convection associated with temperature gradients may enable a cycle in which oligomers formed in high-temperature regions are transported to lower-temperature regions and preserved. This study suggests that mineral-catalyzed oligomerization can occur on Europa's seafloor, and that the combination of temperature gradients and water-rock interactions may enable further abiotic polymerization of organic molecules.