Atropisomerism in a polyglutamate-based thermoresponsive alignment medium.

Structure elucidation via residual dipolar couplings (RDCs) relies on alignment media. We report on lyotropic liquid crystals (LLCs) of poly-γ-p-biphenyl(2'-methoxy-2-methyl)methyl-L-glutamate (PBPM3LG). Temperature dependent atropisomerism within the biphenyl group enables the acquisition of multiple RDC-datasets within one sample.

Investigations of the Alignment Process of PBPMLG: 2 H NMR Analysis Reveals a Thermoresponsive 90° Flip of the Polymer.

The application of anisotropic parameters in NMR-spectroscopy enables the acquisition of spatial and angular information, complementary to those from conventional isotropic NMR-measurements. The use of alignment media is a well-established method for inducing anisotropy. PBPMLG is a recently discovered polyglutamate-based alignment medium, exhibiting thermoresponsive behavior in the lyotropic liquid crystalline (LLC) phase, thus offering potential for deeper understanding of the alignment process. We present one approach for investigating the thermoresponsive behavior by synthesizing specifically deuterated PBPMLG-isotopologues and their subsequent analyses using 2 H NMR-spectroscopy. It was possible to relate the observed thermoresponsive behavior to a flip of the polymer with respect to the external magnetic field-an effect never observed before in glutamate-based polymeric alignment media. Furthermore, a solvent-induced temperature dependent gelation was verified in THF, which might provide yet another opportunity to manipulate the properties of this alignment medium in the future.