Synthesis, Characterization, and Double Layer Capacitance Charging of Nanoclusters Protected by 6-Mercaptopurine

Abstract

The synthesis of gold nanoparticles by using the one-phase method of Brust has been carried out in this work to obtain 6-mercaptopurine monolayer protected gold nanoclusters (6MP-MPCs). The 6MP-MPCs are somewhat polar clusters that are soluble in polar solvents such as DMF and DMSO and in neutral and alkaline aqueous solutions. The average size of the clusters is 2.4 ± 0.5 nm and a stoichiometry of Au459(6MP)62 has been established by taking into account high resolution transmission electron microscopy, X-ray diffraction, and thermogravimetric analysis results of the 6MP-MPCs. The mode of binding of the 6MP molecules to the gold surface has been studied by FT-infrared and X-photoelectronic spectroscopies that evidence the existence of the S−Au interaction. Moreover, the different tautomers of the 6MP molecules in homogeneous solution suffer the transformation into the thiol N(9)H tautomer in the adsorbed state. Finally, taking together the size of these MPCs with the low effective dielectric constant of the 6MP monolayer in contact with the DMF solution makes the observation of the quantized charging of the double layer of these 6MP-MPCs possible. A capacitance value of 1.06 aF consistent with the core dimension and protective monolayer dielectric properties has been determined for the individual 6MP-MPCs.