Herein we report for the first time the supramolecular hydrogelation of a derivative of 3-nitrotyrosine (3-NT), which is an oxidized byproduct of tyrosine, produced in the presence of reactive nitrogen species in the cell. The 9-fluorenylmethyloxycarbonyl (Fmoc) derivative of 3-NT, FNT, can form self-supported hydrogels at a wide range of pH values (4.5-8.5) in 50 mM phosphate buffer solutions. Hydrogels prepared at pH 7.0 are yellow, transparent, and thixotropic in nature. A yellow hydrogel was obtained by changing the pH from 4.5 to 8.5. Moreover, the gelation efficiency of the FNT gelator was enhanced by lowering the pH of the buffer solution. pH-Dependent self-assembly properties of the gelator were studied by using UV-vis, fluorescence, and circular dichroism spectroscopy and wide-angle X-ray diffraction techniques. Field-emission-scanning electron microscopy and transmission electron microscopy studies of the self-assembled FNT hydrogel showed a nanofibrillar network structure. Interestingly, the hydrogel showed injectable behavior at physiological pH. The low cytotoxicity value and high antimicrobial properties of the hydrogel indicated that it is a potential material for biomedical applications.
Keywords: antimicrobial activity; hydrogel; modified aromatic amino acid; self-assembly; thixotropic; tyrosine.