Proton-decoupled carbon-13 NMR spectroscopy in a lyotropic chiral nematic solvent as an analytical tool for the measurement of the enantiomeric excess
Résumé
Organic solutions of poly-ç-(benzyl-L-glutamate) (PBLG) generate a sufficient differential ordering effect (DOE) to discriminate enantiomers using proton decoupled carbon-13 NMR in natural abundance. Discrimination between enantiomers is observed through the carbon-13 chemical shift anisotropy (CSA) differences. This method is successfully applied to a large number of chiral molecules including a case of axial chirality and offers the advantage that no labeling or chemical modification of molecules is needed. In most cases, the chemical shift differences are large enough to measure the enantiomeric excess with accuracy. We show that this new tool is an attractive and powerful alternative to the existing enantiomeric analytical techniques.