Development of novel supramolecular alignment media based on 1,3,5-benzenetricarboxamides (BTAs)

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In recent years residual dipolar couplings became more and more important in protein as well as organic structure elucidation. Alignment media play a key role in this respect: Dipolar couplings are anisotropic NMR interactions, which are not observable under isotropic conditions. Thus, NMR experiments for the observation of anisotropic NMR interactions are usually conducted either in liquid crystals or in anisotropically swollen gels. Most systems used so far have in common, that they are based on classic polymeric materials. This leads to significant challenges as far as a complicated and/or time consuming preparation and purification is concerned. To provide a solution for this problem we have developed the first lyotropic liquid crystals based on supramolecular polymers in organic solvents, which can be used as alignment media. The 1,3,5-benzene tricarboxamides (BTAS) used for this purpose are monomeric compounds of low molecular weight, which self-assemble in solution to large stacks (due to hydrogen bonding and pi-pi-stacking). These stacks behave – in the broader sense – analogously to classic polymeric chains, including their form anisotropy which is necessary for the establishment of a liquid crystalline behavior.A formidable challenge in the application of supramolecular polymers as alignment media is the dynamic nature of the underlying self-association process: disturbing effects of the solvent, the analyte or of impurities can have a negative impact on the self-association process and thus on the alignment medium obtained. This can even lead to the break-down of anisotropic properties. One starting point to alleviate these difficulties is the structure of the BTA used. It contains a core, which is mainly responsible for the self-assembly and a substituent, which can – in principle - be chosen freely. Starting points for a clever choice of substituents are provided by the literature. The aim of this research project is thus the preparation and testing of known, as well as the development of novel substituted BTAs for the use as alignment media in organic solvents to establish a versatile alternative to the known polymer-based systems.