Gamma radiolysis stability of citric acid-Fe3+-montmorillonite complexes: Implications for prebiotic chemistry

Iron is widely distributed in natural environments and ubiquitous in clay minerals, which likely played a key role in abiotic processes on early Earth and some extraterrestrial bodies. To further understand this, we investigated the stability of citric acid-Fe 3+ -montmorillonite (CA-Fe-Mnt) complexes under gamma irradiation, highlighting their potential importance in prebiotic chemistry. Specifically, we studied the sorption dynamics between Fe 3+ -montmorillonite (Fe-Mnt) and citric acid (CA) at pH 2 and 6 for different time intervals (15–60 min) and tested for possible desorption using 0.1 mol L -1 CaCl 2 . ESI-HPLC-MS, ATR-FTIR, and XRD analyses revealed that CA chemisorbs onto Fe-Mnt, forming a stable, desorption-resistant complex, likely due to its strong coordination with interlayered iron cations. While citric acid in aqueous solution (5 x10 -4 mol L -1 ) is highly susceptible to indirect water radiolysis persisting less than 2% at 20 kGy, the CA-Fe-Mnt complex demonstrated robust stability under gamma irradiation (up to 40 kGy). However, the mineral matrix exhibited signs of structural degradation, evidenced by the loss of Si-O signal intensity observed by ATR-FTIR. This suggests that the organic matter is preserved at the cost of the mineral’s structural order, which appears to dissipate the absorbed radiation through lattice degradation. These results suggest that clay-organic complexes may be a means of preserving organic matter in highly irradiated environments ( e.g ., hydrothermal systems, impact sites, and early Mars surfaces), providing new insights into the geochemical mechanisms of prebiotic preservation. • Citric Acids forms a stable, non-desorbable complex with Fe 3+ -montmorillonite • Optimal Citric Acid sorption on Fe 3+ -clay occurs at pH 6 via HCit 2- coordination • The CA-Fe-Mnt complex resists gamma radiolysis, retaining ∼35% CA at 40 kGy • Fe-clay complexes are a geochemical preservation system for prebiotic environments