In-situ observation of the crystallization behavior of L-excess amino acid solutions under high pressure and the possibility of enantiomeric enrichment

Abstract

A slight excess of L-amino acids has been reported in meteorites, and its origin is attributed to circularly polarized ultraviolet light in space, but the origin of homochirality remains unclear. This study investigated the possibility of L-amino acid enrichment under high-pressure conditions inside an icy planet to clarify how enantiomeric condensation occurred. Aqueous solutions containing L-alanine and D-alanine in different ratios were pressurized to 3 GPa, and the precipitation of alanine crystals and high-pressure phases of ice, VI and VII, were observed in situ by measuring X-ray diffraction patterns. DL-alanine precipitated from the solutions with L:D ratios of 7:3, 6:4, and 5:5. Despite the excess of L-amino acids, no L-alanine crystals were observed. This study suggests that enantiomeric enrichment may occur associated with DL-alanine precipitation.