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Chiral Purity of Crystals Using Low‐Frequency Raman Spectroscopy
Author(s) -
Nemtsov Irena,
Mastai Yitzhak,
Tischler Yaakov R.,
Aviv Hagit
Publication year - 2018
Publication title -
chemphyschem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.016
H-Index - 140
eISSN - 1439-7641
pISSN - 1439-4235
DOI - 10.1002/cphc.201800739
Subject(s) - enantiopure drug , raman spectroscopy , enantiomeric excess , enantiomer , chirality (physics) , raman optical activity , circular dichroism , vibrational circular dichroism , racemic mixture , materials science , chiral resolution , spectroscopy , hydrogen bond , chemistry , crystallography , analytical chemistry (journal) , organic chemistry , chiral symmetry , molecule , enantioselective synthesis , optics , catalysis , physics , quantum mechanics , quark , nambu–jona lasinio model
The pharmaceutical industry is in need of new techniques to identify the chirality of solids due to regulatory and safety concerns regarding the biological activity of enantiomers. In this study, we present for the first time the application of low‐frequency Raman spectroscopy as a new and sensitive method for analyzing the chiral purity of crystals. Using this method, we were able to identify small amounts, as low as 1 % w/w, of an enantiomer in racemic crystals. To demonstrate the capabilities of the method, we used a model system based on chiral crystals of enantiopure, racemic crystals and their mixtures in various ratios. We found that the low‐frequency Raman spectra of racemic and enantiopure crystals are significantly different, reflecting the different hydrogen bond networks. Moreover, a comparison of the sensitivity of enantiomeric excess in chiral crystals to that of circular dichroism and X‐ray diffraction measurements showed that low‐frequency Raman attains high sensitivity comparable to chiral optical methods used for solutions. Overall, our proposed approach of using Raman spectroscopy for determining enantiomeric excess in crystals is simple, fast, and offers a high degree of chiral sensitivity.