Three-Component Supramolecular System with Multistimuli-Responsive Properties in Water

Area of Science:

• Supramolecular Chemistry
• Polymer Science
• Materials Science

Background:

• Hyperbranched polyethylenimine terminated with isobutyramide groups (HPEI-IBAm) is a versatile polymer scaffold.
• 4-(phenylazo)benzoic acid (PABA) is an azobenzene derivative capable of photoisomerization.
• α-cyclodextrin (α-CD) is a cyclic oligosaccharide known for its host-guest complexation abilities.

Purpose of the Study:

• To assemble and characterize three-component supramolecular complexes of HPEI-IBAm, PABA, and α-CD.
• To investigate the thermoresponsive properties of these complexes, focusing on cloud point temperature (Tcp).
• To explore the influence of component concentrations, pH, and photoisomerization on the complex's behavior.

Main Methods:

• Formation of three-component supramolecular complexes at pH≈7.
• Characterization using NMR spectroscopy ((1)H and 2D ROESY).
• UV/Vis spectrometric titration to assess complex stoichiometry and binding.
• Cloud point temperature (Tcp) measurements to evaluate thermoresponsive behavior.
• Photoisomerization studies using UV/Vis light irradiation.

Main Results:

• Successful assembly of HPEI-IBAm/PABA/α-CD supramolecular complexes confirmed by NMR.
• Complexation studies indicated limited α-CD content and incomplete PABA complexation.
• The complexes exhibited thermoresponsive behavior, with Tcp significantly affected by α-CD concentration, PABA concentration, and pH.
• Increasing α-CD concentration initially caused a sharp rise in Tcp, followed by a gradual increase.
• pH variations (≈7 to ≈9) had differential effects on Tcp depending on α-CD concentration.
• Trans-to-cis photoisomerization of PABA units decreased the Tcp, a different outcome compared to two-component systems.

Conclusions:

• The three-component supramolecular complexes demonstrate tunable thermoresponsive properties.
• The interplay between component ratios, pH, and photoisomerization offers a pathway for designing smart materials.
• Photoisomerization of azobenzene moieties provides a light-triggered mechanism to modulate the complex's aqueous behavior.