Chiral Nanoparticle-Induced Enantioselective Amplification of Molecular Optical Activity

Abstract

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.