Inversion of Optical Activity in the Synthesis of Mercury Sulfide Nanoparticles: Role of Ligand Coordination.

Optical activity in inorganic colloidal materials was controlled through interactions of chiral molecules with the nanoparticle (NP) surface. An inversion of optical activity in the synthesis of mercury sulfide (HgS) NPs was demonstrated with an intrinsically chiral crystalline system in the presence of an identical chiral capping ligand. A continuous decrease in the positive first Cotton effect and an eventual reversal of CD profile were observed upon heating the aqueous solution of HgS NPs capped with N-acetyl-l-cysteine (Ac-l-Cys) at 80 °C. Ac-l-Cys afforded two bidentate coordination configurations with an almost mirror image of each other using the thiolate and either of carboxylate or acetyl-carbonyl groups on the HgS core. Experiment and calculation suggest that a shift in the distribution of the NP formation with energy in response to the combinations of ligand coordination structure and chiral crystalline surface is responsible for the inversion of optical activity.