Double-responsive polyampholyte as a nanoparticle stabilizer: application to reversible dispersion of gold nanoparticles

Water-soluble and durable Au nanoclusters, smaller than 4 nm with a narrow size distribution, were supported on a pH-and solvent-responsive water-soluble polyampholyte (SPES). Such synthesized Au@SPES hybrids possessed clear pH-and solvent-sensitive properties, and exhibited precipitation behaviors in response to pH and solvent changes in aqueous solution. Furthermore, the recycled catalyst could be redissolved in water for reuse via simple procedures based on the pH-sensitivity of the polyampholyte. By employing such catalysts, aerobic oxidation of alcohols should be able to be carried out in a homogeneous manner and may thus give rise to similar catalytic activities and selectivities as the homogeneous parent system. The phase separation and sensitivity of the SPES-stabilizing Au nanoclusters permitted a facile separation of the clusters from the reaction mixture without any negative aggregation.