Effect of the L-DOPA hydroxyl groups in the formation of supramolecular hydrogels

Fmoc-L-DOPA-D-Oxd-OH was prepared starting from commercially available L-DOPA. Its gelation ability was tested as a comparison with Fmoc-L-Tyr-D-Oxd-OH and Fmoc-L-Phe-D-Oxd-OH using ten different triggers. Among them, only GdL, CaCl2 and ZnCl2 form strong hydrogels with the three gelators. The analysis of the aerogels obtained by hydrogels freeze drying show that the three gelators induce always the formation of dense networks, that strongly depend on the gelator nature. The rheological analysis of these samples demonstrate that the stronger gels are obtained with the L-Tyr containing gelator, while the L-DOPA containing hydrogels are characterized by a storage modulus approximately an order of magnitude lower. Finally, the L-Phe containing gelator show a different trend respect to the other ones depending on the trigger. All the hydrogels show a thixotropic behaviour at the molecular level. These results indicate that the hydrogel formation is sensitive both to the number of the hydroxyl moieties on the aromatic rings and on the trigger nature.