Lyotropic Liquid Crystals based on Bisperylene Imides as Alignment Medium for Obtaining Anisotropic NMR Parameters

Measurement of anisotropic parameters, such as Residual Dipolar Couplings (RDCs) and Residual Chemical Shift Anisotropies (RCSAs), have played an important role in structural refinement of organic compounds. A key factor for the obtention of these parameters is the selection of an appropriate alignment medium. Lyotropic liquid crystals, among other systems, have been considered a good alternative for this purpose. We present here three new water-compatible aligning media based on mesogenic bisimides derived from the conjugation of perylenetetracarboxylic dianhydride with the aminoacids L-valine (BPI-LVal), L-leucine (BPI-LLeu) and Glycine (BPI-Gly). We studied the influence of the concentration and the temperature on the formation of the mesophase by monitoring the splitting of the quadrupole coupling of the D2O signal in the 2H NMR spectra. It was determined that the best conditions for using these mesophases as alignment medium corresponds to a solution of 0.5 M at 23ºC for BPI-LVal, 0.3 M at 27ºC for BPI-LLeu, and 0.2 M at 25ºC for BPI- Gly. To evaluate the efficiency of the three nematic phases as alignment media, we used sucrose as a test molecule. The experimental RDCs values were in the range of -54 to 75 Hz, while RCSA values a range of -0.32 to +0.18 ppm were obtained, providing good quality factors that allowed us to study the conformation of sucrose in aqueous solution.
Acknowledgements
The authors thanks: Brazilian National Council for Scientific and Technological Development, CNPQ, (426216/2018-0; 311683/2019-3; 304662/2022-4) and Universidade Federal de Pernambuco for financial support. We thank also Centro de Tecnologias Estratégicas do Nordeste (CETENE) for computer time through support of Fundação de Amparo à Ciência e Tecnologia do Estado de Pernambuco, FACEPE, (APQ- 1864-1.06/12). DGBS thanks CAPES for a doctoral fellowship.