Water-driven stabilization of diphenylalanine nanotube structures

L,L-diphenylalanine has been employed in the formation of self-assembled peptide nanotubes with great potential for the development of biosensors, molecular carriers, and optoelectronic devices. They are usually formed in an aqueous solution, and it is well known that water remains confined inside the structure. However, the role played by water in the overall stability of the nanotube is still unknown at the microscopic level. In this work, we investigate the stability of peptide structures after assembly due to the interaction with water molecules. We demonstrate, using molecular dynamics based on density functional tight-binding techniques, that water is fundamental in keeping the nanotube structure. It interacts with the nanotube walls as well as with other water molecules via hydrogen bonds keeping the structure stable. We identify and quantify the interaction between water and the relevant groups, and, upon increasing the solvent concentration, we show there is a transition region where there is a competition between the formation of water/water hydrogen bonds, and steric effects.