Insight on the NMR study of supramolecular gels and its application to monitor molecular recognition on self-assembled fibers

The H-1 NMR study of supramolecular gels formed by two organogelators derived from valine is described. The analysis of the variation of chemical shift values and relaxation times in the gel samples reveals that in these systems only discrete species are observed by H-1 NMR. The reduced T-2 values and negative NOEs that are measured upon gel formation can be ascribed to an exchange between discrete organogelator species and the gel network. This process is found to be fast in the time scale of H-1 NMR relaxation and slow in the NMR observation frequency time scale. It is shown here that other molecules, aside from the gelator itself, can interact with the gel network and this process can be monitored easily by measurement of relaxation times. As a proof of principle, the selective interaction of 2,2'-bis(hydroxymethyl) biphenyl over diphenylmethane with the self-assembled fibers formed by one of the gelators in benzene is described.