Building up nanotubes: docking of "Janus" cyclodextrins in solution

Area of Science:

• Supramolecular Chemistry
• Computational Chemistry
• Physical Chemistry

Background:

• Cyclodextrins are cyclic oligosaccharides with unique host-guest properties.
• Janus cyclodextrins (JCD) possess distinct chemical modifications on their rims, influencing their behavior.
• Understanding JCD self-assembly in solution is crucial for designing novel nanomaterials.

Purpose of the Study:

• To investigate the self-association behavior of Janus 6-amino-6-deoxy-2O-carboxymethyl-beta-cyclodextrins (JCD) in aqueous solutions.
• To characterize the stability and structural properties of JCD dimers and trimers.
• To explore the formation of nanotube-like structures from JCD aggregates.

Main Methods:

• Molecular dynamics (MD) simulations were employed to analyze JCD-JCD interactions.
• Free energy calculations were performed to quantify the stability of JCD dimers.
• Structural and dynamical properties of JCD aggregates and trapped water were analyzed.

Main Results:

• JCD dimers exhibit a stable docking configuration with a free energy minimum of approximately -45 kcal mol(-1).
• JCD trimers in solution are remarkably stable, showing minimal distortions.
• Geometrical analysis indicates the formation of flexible nanotubes with water exchange capabilities between the central channel and bulk solution.

Conclusions:

• JCD molecules self-assemble into stable dimeric and trimeric structures in aqueous solutions.
• These assemblies display characteristics of flexible nanotubes, suggesting potential applications in molecular encapsulation and transport.
• The properties of water confined within these JCD nanotubes are significantly influenced by the charge distribution at the JCD rims.