A Balance between van der Waals and Cation-π Interactions Stabilizes Hydrophobic Assemblies

Area of Science:

• Materials Science
• Supramolecular Chemistry
• Nanotechnology

Background:

• Designing stable molecular self-assemblies in aqueous environments is challenging.
• Hydrophobic interactions, van der Waals (vdW) forces, and cation-π interactions are key to stabilizing such structures.
• Thermal stability is a critical parameter for practical applications of molecular assemblies.

Purpose of the Study:

• To develop a thermally stable molecular self-assembly (nanocube) in water.
• To investigate the role of amphiphile structure and substituents on thermal stability.
• To elucidate the contribution of vdW and cation-π interactions to the stability of hydrophobic assemblies.

Main Methods:

• Synthesis of gear-shaped amphiphiles (GSAs) with indented hydrophobic surfaces.
• Formation of nanocube self-assemblies in water.
• Thermal decomposition analysis to determine stability.
• Systematic modification of GSA structure by introducing substituents.

Main Results:

• A highly thermally stable nanocube (decomposition temperature 415 K) was successfully assembled in water.
• Introduction of an electron-donating substituent increased the decomposition temperature by 12 K.
• The position of the substituent significantly impacted thermal stability, highlighting the importance of molecular meshing and cation-π interactions.
• The nanocube is stabilized by vdW, cation-π, and hydrophobic interactions.

Conclusions:

• Gear-shaped amphiphiles with indented hydrophobic surfaces enable the formation of highly thermally stable nanocubes in water.
• Tuning substituents on the amphiphile structure can significantly enhance thermal stability.
• Both precise molecular meshing (vdW interactions) and cation-π interactions are critical for improving the thermal stability of these hydrophobic assemblies.