Hydrogel formation using new L-lysine-based low-molecular-weight compounds with positively charged pendant chains

Low-molecular-weight compounds based on L-lysine with alkylpyridinium or-imidazolium groups have been synthesized and studied for their gelation behavior in H2O. Most compounds formed gels below a concentration of 2.5 weight-%, the pyridinium bromide 2a and the 1-methyl-1H-imidazolium bromide 3 even at 0.1 weight-%. The minimum gel concentration (MGC) necessary for hydrogelation increased with increasing length of the Lys N-alpha-alkanoyl chain, but the gelation ability concomitantly decreased. Electron-microscopic images demonstrated that these hydrogelators create a three-dimensional network in H2O by entanglement of self-assembled nanofibers. A fluorescence study with 8-anilinonaphthalene-1-sulfonic acid (ANS) proved that some hydrophobic aggregates are formed at hydrogelator concentrations below an MGC of less than 50 mum (0.004%). FT-IR, H-1-NMR, and Fluorescence studies indicated that the driving forces for the self-assembly into nanofibers are mainly hydrophobic interactions and H-bonding between amide groups.