Temperature-Dependent and pH-Responsive Pillar[5]arene-Based Complexes and Hydrogen-Bond-Based Supramolecular...

Area of Science:

• Supramolecular Chemistry
• Hydrogen Bonding
• Host-Guest Chemistry

Background:

• Supramolecular systems in water are crucial, but those utilizing hydrogen bonds are rare.
• Pillar[5]arene derivatives are known for forming host-guest complexes.

Purpose of the Study:

• To synthesize and characterize the first hydrogen-bond-based supramolecular pentagonal boxes (SPBs) stable in aqueous media.
• To investigate the pH-responsiveness and guest encapsulation properties of these novel SPBs.

Main Methods:

• Synthesis of per-dimethylamino-pillar[5]arene (1) and bis-sulfonate guests (2a-c).
• Formation of SPBs using 1, benzene polycarboxylic acids (3a,b) as lids, and guests (2a-c).
• Characterization using temperature and pH-dependent studies, and 1H NMR spectroscopy.

Main Results:

• Successfully formed stable, water-soluble SPBs (1(3a)2 and 1(3b)2) through hydrogen bonding.
• Demonstrated that guest encapsulation is dependent on temperature, pH, and the nature of the lid compounds.
• Observed distinct 1H NMR spectral differences for guests within the pillar[5]arene cavity and the SPBs.

Conclusions:

• The study reports the first example of hydrogen-bond-based SPBs that are stable in water.
• These SPBs exhibit pH-responsiveness and tunable guest binding properties.
• The findings offer new possibilities for designing sophisticated supramolecular architectures in aqueous environments.