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 vari-ations of self-assembled structures are attainable through pH variation ofunmodified diphenylalanine in trifluoroethanol. The obtained self-assembleddiphenylalanine nanostructures are found to vary drastically with pH, incu-bation time, and diphenylalanine concentration in solution. The observedstructures ranged from structured films at neutral and alkaline conditions tovertically 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. Thisalso emphasizes the importance of the dipole moment for the resulting self-assembled structures. Our results suggest that, in comparison to the commonlydescribed procedure of diphenylaniline nanowire growth through anilinevapor treatment, strictly anhydrous conditions are not necessarily required.