Chiral Imprinting on Inorganic Nanoparticles for Enantioselective Surface Recognition

Chiral semiconductor nanoparticles, especially metal oxides, hold great potential for selective photocatalysis and enantiomer separation. Chirality in such systems can emerge during nanoparticle nucleation and growth, leading to optical activity in the absorption range of the material. A key aspect of this phenomenon is the transfer of chirality from a chiral organic molecule interacting with the nanoparticle surface to the inorganic core. In this study, threoninol is used as a chiral ligand to induce chirality in titanium dioxide (TiO₂) nanoparticles, and its binding mode to the metal oxide is investigated through nuclear magnetic resonance (NMR) spectroscopy. The analysis reveals that threoninol interacts with the TiO₂ surface primarily via hydrogen bonding through its hydroxyl groups. To determine whether a chiral imprint is retained, the ligand is fully removed using ultraviolet (UV) irradiation, and the nanoparticles are subsequently re-exposed to a racemic mixture of threoninol. Remarkably, the nanoparticles selectively re-bind the enantiomer used in the original synthesis. This provides evidence for the presence of enantioselective active sites on the TiO₂ surface, suggesting that the chiral ligand imprints chirality through structural features. Although the precise mechanism of chiral imprinting remains speculative, the findings demonstrate that inorganic nanomaterials can be endowed with enantioselective properties.