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Distinguishing Enantiomers by Tip‐Enhanced Raman Scattering: Chemically Modified Silver Tip with an Asymmetric Atomic Arrangement
Author(s) -
Sukmanee Thanyada,
Wongravee Kanet,
Kitahama Yasutaka,
Ekgasit Sag,
Itoh Tamitake,
Pienpinijtham Prompong,
Ozaki Yukihiro
Publication year - 2020
Publication title -
angewandte chemie
Language(s) - English
Resource type - Journals
eISSN - 1521-3757
pISSN - 0044-8249
DOI - 10.1002/ange.202005446
Subject(s) - enantiomer , raman scattering , chemistry , electric field , raman spectroscopy , molecule , chirality (physics) , hydrogen bond , analytical chemistry (journal) , stereochemistry , organic chemistry , chiral symmetry , optics , physics , nambu–jona lasinio model , quantum mechanics , quark
Discrimination between enantiomers is achieved by tip‐enhanced Raman scattering (TERS) using a silver tip that is chemically modified by an achiral para ‐mercaptopyridine ( p MPY) probe molecule. Differences in the relative intensities of the p MPY spectra were monitored for three pairs of enantiomers containing hydroxy (−OH) and/or amino (−NH 2 ) groups. The N: or N + −H functionality of the p MPY‐modified tip participates in hydrogen‐bond interactions with a particular molecular orientation of each chiral isomer. The asymmetric arrangement of silver atoms at the apex of the tip induces an asymmetric electric field, which causes the tip to become a chiral center. Differences in the charge‐transfer (CT) states of the metal‐achiral probe system in conjunction with the asymmetric electric field produce different enhancements in the Raman signals of the two enantiomers. The near‐field effect of the asymmetric electric field, which depends on the number of analyte functional groups capable of hydrogen‐bond formation, improves the degree of discrimination.