Cationic surfactant-triggered formation of a supramolecular hydrogel by a negatively charged L-valine derivative

Octadecylaminocarbonyl-L-valyl-N-suberic acid sodium salt (1), prepared from octadecylaminocarbonyl-L-valine, has been found to function as a cationic surfactant-triggered hydrogelator. Although 1 was water-soluble and had no hydrogelation ability, it formed a hydrogel in the presence of a cationic surfactant. Hydrogelation at room temperature occurred by addition of a cationic surfactant solution to an aqueous solution of 1. FT-IR studies demonstrated that the driving forces for hydrogelation were non-covalent intermolecular interactions such as hydrophobic and hydrogen bonding interactions. In addition, fluorescence spectroscopy using 8-anilino-1-naphthalenesulfonic acid sodium salt (ANS) as a probe demonstrates that some aggregates such as micelles play an important role in the self-assembly of 1 into nanofibers. Moreover, it was found that the combination of 1 and dodecyl(trimethyl) ammonium chloride (DTMACl) provided a suitable hydrophobic-hydrophilic balance, and formed a thermally stable hydrogel.