Thermoreversible Gelation of Homopolyglutamates PBPMLG, PBPELG, and PBPHLG: Another Step toward de Novo RDC-Based Structure Elucidation

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.