Stability of adenine in interaction with saponite in a simulated hydrothermal impact-generated system and its implications for astrobiology

Abstract

For astrobiological studies related to the chemical evolution of organic molecules, it is essential to establish a plausible geological context, either on early Earth or at another viable site within the solar system. Impact-generated hydrothermal systems may have provided an ideal environment for prebiotic chemical reactions before the origin of life.

In this study, we simulated the conditions of such systems using saponite, a clay mineral identified as a product of hydrothermal alteration in impact craters that once hosted hydrothermal activity. Adenine was chosen as the model organic molecule due to its biological relevance and its known abiotic formation, as evidenced by its detection in certain meteorites. The interaction between saponite and adenine was investigated by analyzing adsorption kinetics and isotherms, revealing that adsorption is favored at acidic pH (3.5), as under these conditions, approximately 97 % of the adenine is adsorbed. The interaction between the molecule and the clay was observed through spectroscopic techniques such as XRD, FRX, Raman and ATR-FTIR, UV–vis spectrophotometry, and HPLC-UV chromatographic. Additionally, thermolysis experiments were conducted on aqueous adenine solutions and adenine-saponite mixtures. The results indicate that saponite plays a protective role, preventing adenine decomposition at temperatures ranging from 100 °C to 200 °C across a pH range of 3.5–8.9. These processes are critical for astrobiology, as they demonstrate how some clay minerals could have concentrated and preserved prebiotic organic molecules on early Earth, Mars, or planetesimals, facilitating the emergence of life.