Chiral Nanoparticle-Induced Enantioselective Amplification of Molecular Optical Activity

Enantiodifferentiation is of fundamental importance in chiral chemistry and substantially requires high optical activity (OA) of enantiomers; but the enantiomeric OA is typically weak due to subwavelength molecular dimension, leading to a lack of sensitive enantiodifferentiation. A new approach is devised to evidently amplify the enantiomeric OA by anchoring axially chiral molecules containing the binaphthyl chromophore on silver chiral nanoparticles (AgCNPs) with a sub-5 nm helical pitch (P). Compared to the OA of dissolved enantiomers, that of (R)- and (S)- enantiomers can be enantioselectively amplified on right-handed and left-handed AgCNPs, respectively, in as high as one order of magnitude. The enantioselective amplification is probably ascribed to the enantiospecific adsorption-induced change in the dihedral angle of the binaphthyl chromophore, resulting from chirality transfer from chiral footprints of the AgCNPs to the binaphthyl chromophore through the Ag-S bicontacts. The enantioselective amplification tends not to occur as long as P > 5 nm or on achiral Ag nanoparticles, due to a lack of the chirality transfer. This work imposes the significant application of enantiodifferentiation, which is on practical demand for producing single-enantiomer pharmaceutics and pesticides with no fatal adverse effect, on the emerging chiral metamaterials composed of metallic CNPs.