Charge-Transfer-Induced Enantiomer Selective Discrimination of Chiral Alcohols by SERS

Abstract

In our previous study, we proposed a label-free enantioselective discrimination methodology for chiral alcohols based on surface-enhanced Raman scattering (SERS) spectroscopy. This method does not use either chiral reagents or circularly polarized light (chiral light). In the present study, a series of SERS experiments were carried out with an achiral SERS probe molecule, p-aminobenzenethiol (PATP), as the chiral selector molecule to develop this method further and to explore the possible mechanism of enantioselective discrimination. The relative intensities of the nontotally symmetric (b2 mode) bands in the SERS spectra of PATP change depending on the presence of different enantiomeric environments, which is a manifestation of charge transfer (CT) processes. From laser excitation wavelength-dependent and concentration-dependent SERS experiments, we have further verified that this CT-induced chiral discrimination magnifies the differences between two chiral alcohol enantiomers interacting with PATP by SERS technology. We propose that the directions of CT from Ag nanoparticles to PATP molecules are different in different enantiomeric conditions, which results in differences in the CT transitions and significantly different SERS spectra. Therefore, this work allows discrimination between two enantiomers and breaks the traditional notion that chiral discrimination requires other chiral entities as chiral selectors or the involvement of chiral light in the system. We envision that this approach will be of great significance in the field of chiral separation and chiral catalysis.