Catalytic reduction of 4-nitrophenol with gold nanoparticles stabilized by large-ring cyclodextrins

The synthesis of gold nanoparticles stabilized in an aqueous phase by cyclodextrins (CD) was performed. The solvent-dispersed nanoparticles were characterized by transmission electron microscopy, UV-vis spectroscopy and dynamic light scattering analysis. Nanoparticles stabilized with large-ring CD composed of 9 or more glucose units showed a broader distribution of sizes and a larger hydrodynamic diameter compared to those stabilized with alpha-CD, beta-CD and gamma-CD. Gold nanoparticles stabilized by large-ring CD efficiently reduced 4-nitrophenol to 4-aminophenol with higher reaction rates compared to those stabilized by alpha-CD. NMR analysis proved that no complex formation between 4-nitrophenol and the large-ring CD occurred. The catalytic activities obtained with gold nanoparticles stabilized by large-ring CD were comparable to those observed with beta-CD and gamma-CD confirming their suitability for an efficient stabilization of catalytically active nanoparticles.