Theoretical and experimental aspects of enantiomeric differentiation using natural abundance multinuclear nmr spectroscopy in chiral polypeptide liquid crystals

Abstract

Liquid crystalline organic solutions of poly-γ-benzyl-L-glutamate generate a sufficient differential ordering effect to visualize enantiomers using multinuclear high-resolution NMR spectroscopy at natural isotopic abundance levels. Chiral discrimination can be observed through a difference in the order-sensitive NMR observables, namely: proton–proton, carbon–proton and carbon–carbon residual internuclear dipolar couplings, carbon chemical shift anisotropies, and deuterium quadrupolar splittings. In most cases, the enantiodifferentiation is large enough to allow determation of the enantiomeric excesses satisfactorily. All theoretical considerations and significant experimental parameters that affect the efficiency of this methodology are presented and discussed. The various possible anisotropic NMR techniques provide a very reliable and powerful alternative to the current analytical techniques which operate in the isotropic phase.