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

Abstract

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 2H 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.

Self‐Assembly of Helical Polymers and Oligomers to Create Liquid Crystalline Alignment for Anisotropic NMR Parameters

“…To investigate the influence of backbone and sidechain, various polypeptide‐based homopolymers have been readily obtained using ROP of α ‐amino acid N ‐carboxyanhydride (NCA) monomers in Thiele's group ( Figure a). [ 45–58 ]…”

“…To investigate the influence of backbone and sidechain, various polypeptide-based homopolymers have been readily obtained using ROP of 𝛼-amino acid N-carboxyanhydride (NCA) monomers in Thiele's group (Figure 7a). [45][46][47][48][49][50][51][52][53][54][55][56][57][58] The helicity of polypeptide-based homopolymers is not induced by chiral information in the sidechain but by centrochiral elements in the backbone (Figure 7b). Unexpectedly, they can accommodate a large variety of almost any type of organocompatible analytes, while maintaining their LC properties, Obviously, the diastereomorphous interactions between enantiomers and the polypeptide helices are sufficiently large to provide chiral recognition.…”

“…This not only makes homogenization easier, but also decreases equilibration times to a few minutes in the spectrometer for homogenous orientation (Figure 8c, right). [ 58 ]…”

“…Left: Equilibration of the observed Pake pattern of PBPMLG (TEA initiated); right:Fast equilibration of PBPMLG (DMEA initiated) without noticeable Pake pattern-like formation. Reproduced with permission [57,58]. Copyright 2018, 2021, Wiley-VCH GmbH.…”

Atropisomerism in a polyglutamate-based thermoresponsive alignment medium

“…In our previous work, we introduced various polymer-based LLC alignment media, responsive to external stimuli such as magnetic fields or temperature. 6 Poly-g-p-biphenylmethyl-Lglutamate (PBPMLG) 7,8 called parent polymer here and its derivates poly-g-p-biphenylethoxy-L-glutamate (PBPELG) and poly-g-p-biphenylhexoxy-L-glutamate (PBPHLG) 9 have shown promising results when applied in RDC- [10][11][12] based structure elucidation of small organic compounds.…”