The Many Faces of Diphenylalanine

Diphenylalanine is well known to form complex self-assembled structures, including peptide nanowires, with morphologies depending on N- and C-terminal modifications. Here we report that significant morphological variations of self-assembled structures are attainable through pH variation of unmodified diphenylalanine in trifluoroethanol. The obtained self-assembled diphenylalanine nanostructures are found to vary drastically with pH, incubation time, and diphenylalanine concentration in solution. The observed structures ranged from structured films at neutral and alkaline conditions to vertically aligned nanowires and sponge-like structures at acidic conditions. These observations are corroborated by the results of electrostatic modelling, indicating the disappearance of the dipole moment at high pH values. This also emphasizes the importance of the dipole moment for the resulting self-assembled structures. Our results suggest that, in comparison to the commonly described procedure of diphenylaniline nanowire growth through aniline vapor treatment, strictly anhydrous conditions are not necessarily required.