Spontaneous Emergence of Homochiral Suspensions from Racemic Solutions via Stochastic Nucleation.

Homochirality represents a hallmark of life, and its emergence on the prebiotic Earth remains elusive. Here, we demonstrate a spontaneous pathway to homochirality, where a conglomerate-forming chiral species (-(2-methylbenzylidene)-phenylglycine amide, NMPA) evolves from an initial perfectly symmetric state, i.e., a racemic solution, to a fully homochiral state, where only enantiopure crystals of one handedness are present in the suspension. It entails first the establishment of supersaturated conditions, e.g., because of either solvent evaporation or cooling, then stochastic nucleation of enantiopure crystals as the symmetry-breaking event, and finally asymmetry amplification and complete deracemization via temperature fluctuations in a racemizing solution (thanks to the presence of the base 1,8- diazabicyclo[5.4.0]undec-7-en, DBU). After developing a stochastic modeling platform and an experimental setup, we confirm the plausibility of this pathway through both detailed simulations and laboratory experiments. We also show how from a variety of local homochiral states of different handedness a global homochiral state may emerge via merging and deracemizing. Because the external conditions triggering supersaturation creation, nucleation, and deracemization via temperature-cycling must have existed also on the prebiotic Earth, the proposed spontaneous pathway may have plausibly played a role in the emergence of life on Earth.