Abiotic Enantiomeric Enrichment of Alanine under High Pressure: Investigating a Process for the Origin of Homochirality

Abstract

The origin of homochirality remains an unresolved question, and various hypotheses have been proposed, including selective photodecomposition by circularly polarized ultraviolet light and enantioselective adsorption on mineral surfaces. However, the process by which a slight initial excess of L-enantiomers evolves into the complete dominance of L-forms, as seen in biological systems, has yet to be elucidated. In this study, we measured the solubilities of L-alanine (enantiopure) and DL-alanine (racemic) under high pressure, and found that L-alanine becomes more soluble under high pressure. Furthermore, when mixed solutions with varying L:D ratios were subjected to compression, DL-alanine crystallized preferentially, leaving the excess L-alanine enriched in the liquid phase. These results demonstrate a mechanism in which the difference in solubility between the enantiomer and racemate under high pressure conditions leads to the selective enrichment of L-enantiomers in solution. This finding suggests a novel physicochemical process that could contribute to the emergence of homochirality.