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

A thermally most stable molecular self-assembly in water (nanocube), whose decomposition temperature is 142 °C, has been developed by the design of a gear-shaped amphiphile (GSA) with an indented hydrophobic surface, even though the nanocube is stabilized only by van der Waals (vdW) and cation-pinteractions and the hydrophobic effect. The introduction of an electron-donating substituent in one of the benzene rings in GSA increased the decomposition temperature by 12 K, which is due to the stronger cation-p interactions between the benzene ring and positively charged pyridinium rings and the tighter molecular meshing between the GSAs in the nanocube. It was also found that the position of the substituent introduced in the benzene ring much affects the thermal stability of the nanocubes, indicating that both vdW (molecular meshing) and cation-pinteractions are crucial for the improvement of the thermal stability of the hydrophobic assemblies.