Prebiotic polymer synthesis of lactic and phenyllactic acids under early earth aqueous conditions and their stability against gamma radiation

Abstract

The study of prebiotic polymerization is important to understand the possibility of formation of early compartment, which could lead to become protocell, for prebiotic chemistry to take place. Alpha-hydroxy acids (AHA), a class of prebiotically relevant compounds, undergo polymerization through simple dehydration processes. Upon rehydration, these polymers form membraneless microdroplets (MMD) via phase separation, exhibiting protocell-like properties such as material encapsulation, exchange, motion, coalescence, and evolution into membrane-bound droplets. Despite their astrobiological relevance, key aspects of AHA polymer stability under early Earth conditions remain poorly understood. Specifically, the effects of low aqueous volume, low monomer concentration, and high salinity on polymer formation and MMD assembly have not been thoroughly explored, limiting the understanding of their role in protocell development and the origins of life (OoL). This study investigates the synthesis of phenyllactic acid (PA) and lactic acid (LA) into polymeric gels as prebiotic candidates under dehydration until complete dryness at low concentrations, small reaction volumes, and varying salinities to simulate early Earth conditions. Additionally, their resilience to prebiotic stressors was assessed by gamma-ray radiation exposure to evaluate stability under early Earth conditions and potential material-based Panspermia transfers. Gamma-ray radiation exposure demonstrates the robustness of PA and LA polymer gels to support their viability in extreme environments. Individual analyses of mass spectrometry and microscopy confirmed polymerization of LA and PA at 1 mM, 5 µL and high salinity of 1 M and the subsequent formation of MMDs. These analyses also showed that polyPA and polyLA were robust under 181 kGy of gamma-ray radiation and still able to form MMD. These findings provided insights into prebiotic polymerization and MMD formation under geochemically relevant conditions, contributing to our understanding of the OoL on early Earth and the possibility of interplanetary transport through Panspermia.