Possible Enantioseparation of Racemic Ribose on Chiral Surface Formed by Adsorption of Nucleobases.

The paper proposes a putative prebiotic scenario leading to homochirality in the RNA world. In this scenario, racemic ribose, the only chiral moiety in RNA, was enantioseparated (in its pyranose form) on a chiral surface formed by the adsorption of (prochiral) nucleobases (NBs) on a mineral or metal. Purine bases (adenine and guanine) are more likely candidates for this process than pyrimidine bases because they have more H-bond donors and acceptors. Another possible candidate surface for the enantioseparation of ribose would be formed by the adsorption of nucleobase pairs, e.g., guanine-cytosine (GC). Interactions of ribose molecules with hydrogen bond donors and acceptors of NBs or NB pairs (located on the surface) enforced the orientation of ribose molecules in two directions perpendicular to each other and parallel to the surface. Consequently, the energy of interactions of enantiomers of the sugar with the surface was not the same. Thus, a solvent moving along the surface caused the enantiomers of ribose to move with different rates, resulting in the enantioseparation of ribose in a chromatography-like process. The same process would also separate ribose from other monosaccharides in the mix. Hydrogen bonding between nucleobases was also pivotal in the formation of large homochiral domains on the surfaces.