Smart organic-inorganic hybrids based on the complexation of amino acid-based polymers and water-soluble silsesquioxane nanoparticles

Smart organic-inorganic hybrids were prepared using noncovalent interactions between water-soluble silsesquioxane nanoparticles containing tertiary amine moieties and amino acid-based polymers prepared by reversible addition-fragmentation chain transfer (RAFT) polymerization. Poly(N-acryloyl-4-trans-hydroxy-l-proline) and poly(N-acryloyl-l-proline), or poly(A-Hyp-OH) and poly(A-Pro-OH), respectively, were employed as weak polyelectrolytes, whereas their methylated versions, poly(A-Hyp-OMe) and poly(A-Pro-OMe), were used as thermoresponsive polymers. Simple mixing of aqueous solutions of poly(A-Hyp-OH) and the silsesquioxane nanoparticles led to a straightforward formation of the pH-responsive hybrids, in which a white turbid dispersion was observed at pH = 5-8, whereas transparent solutions were obtained at pH = 2 and 10. The aggregate structures and chiroptical properties of the hybrids were evaluated by scanning force microscopy (SFM) and circular dichroism (CD) measurements. Complex formation with poly(A-Pro-OH) and silsesquioxane nanoparticles was also observed in methanol. Thermoresponsive hybrids were obtained by complexation of the silsesquioxane nanoparticles with poly(A-Hyp-OMe) in water, whereas poly(A-Pro-OMe) showed no specific interaction. To the best of our knowledge, this is the first report of the synthesis of smart organic-inorganic hybrids with pH-responsive and thermoresponsive properties that can be manipulated by the complexation of amino acid-based polymers and water-soluble silsesquioxane nanoparticles.