Efficient Water Self-Diffusion in Diphenylalanine Peptide Nanotubes

Area of Science:

• Biomaterials science
• Nanotechnology
• Physical chemistry

Background:

• Diphenylalanine (FF) nanotubes are self-assembled dipeptide nanostructures with diverse functional properties.
• Nanoconfined water, both bound and free, plays a crucial role in FF nanotube self-assembly and function.
• The precise mechanism of water motion within FF nanotubes was previously unclear.

Purpose of the Study:

• To investigate the sorption properties of FF nanotubes as a microporous material.
• To analyze the self-diffusion of free water within FF nanotube nanochannels at varying temperatures.
• To elucidate the relationship between water cluster size and diffusion behavior.

Main Methods:

• Studied FF nanotube sorption properties.
• Analyzed free water self-diffusion using temperature-dependent measurements.
• Characterized diffusion regimes based on water cluster size.

Main Results:

• Identified a transition in water diffusion regimes within FF nanotubes.
• Observed ballistic diffusion for small water clusters (<5 molecules/unit cell).
• Found Fickian diffusion for larger water clusters, with a diffusion coefficient of 1.3 × 10^-10 m² s^-1 at 40% RH and 30 °C, increasing to 3 × 10^-10 m² s^-1 at 65 °C.

Conclusions:

• Water cluster size dictates the diffusion mechanism in FF nanotube nanochannels.
• The unique water self-diffusion properties suggest potential applications in nanofluidic devices.
• This research adds a new functional dimension to FF nanotube materials.