Quantitative analysis of the stability of Pd dendrimer-encapsulated nanoparticles

The stability of Pd dendrimer-encapsulated nanoparticles (DENs) in air-, N₂-, and H₂-saturated aqueous solutions is reported. The DENs consisted of an average of 147 atoms per sixth-generation, poly(amidoamine) dendrimer. Elemental analysis and UV-vis spectroscopy indicate that there is substantial oxidation of the Pd DENs in the airsaturated solution, less oxidation in the N₂-saturated solution, and no detectable oxidation when the DENs are in contact with H₂. Additionally, the stability improves when the DEN solutions are purified by dialysis to remove Pd ²⁺-complexing ligands such as chloride. For the air- and N ₂-saturated solutions, most of the oxidized Pd recomplexes to the interiors of the dendrimers, and a lesser percentage escapes into the surrounding solution. The propensity of Pd DENs to oxidize so easily is a likely consequence of their small size and high surface energy.