The use of anisotropic NMR parameters-especially residual dipolar couplings (RDCs)-offers access to additional structural information and, therefore, alignment media required for this approach are under a continuous development. Here, we present poly-γ-p-biphenylmethyl-glutamate (PBPMG) as a new versatile enantiodifferentiating alignment medium. The thermoresponsive properties of this polymer allowed for RDC measurements of more than one orientation within the same sample at different temperatures. Moreover, the outstanding enantiodifferentiation along with excellent spectral quality even offered the opportunity to differentiate enantiomers in mixtures.

Residual dipolar couplings (RDCs) offer great potential in modern structure elucidation of organic compounds. Current developments focus on “smart” alignment media, which are able to change the induced alignment via external stimuli to enable de novo structure elucidation. We recently introduced poly-γ-p-biphenylmethyl-l-glutamate (PBPMLG) as a thermoresponsive alignment medium with outstanding enantio­discriminating properties. In this work we present PBPMLG derivates containing spacer groups, separating the biphenyl mesogene of the side chain from the α-helical backbone, with the aim of better understanding the underlying effects and potentially inducing further orientations. Two thermoresponsive effects were observed separately: first, the 90° reorientation of the helix with respect to the external magnetic field and, second, a gelation of the LLC phase. The thermoresponsive gelation has been thoroughly investigated via NMR, polarized optical microscopy, and rheometry. We discuss the implication of the effects observed on RDC-based structure elucidation protocols.

Inherently chiral compounds, such as calixarenes, are chiral due to a nonplanar three-dimensional (3D) structure. Determining their conformation is essential to understand their properties, with nuclear magnetic resonance (NMR) spectroscopy being one applicable method. Using alignment media to measure residual dipolar couplings (RDCs) to obtain structural information is advantageous when classical NMR parameters like the nuclear Overhauser effect (NOE) or Jcouplings fail. Besides providing more accurate structural information, the alignment media can induce different orientations of enantiomers. In this study, we examined the ability of polyglutamates with different side-chain moieties� poly-γ-benzyl-L-glutamate (PBLG) and poly-γ-p-biphenylmethyl-L-glutamate (PBPMLG) �to enantiodifferentiate the inherently chiral phenoxathiin-based thiacalix[4]arenes. Both media, in combination with two solvents, allowed for enantiodiscrimination, which was, to the best of our knowledge, proved for the first time on inherently chiral compounds. Moreover, using the experimental RDCs, we investigated the calix[4]arenes conformational preferences in solution, quantitatively analyzed the differences in the alignment of the enantiomers, and discussed the pitfalls of the use of the RDC analysis.

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