Novel Crown Ether-Capped Cationic Gold Nanoclusters in an Aqueous Medium and Their Single-Electron Charging Features

On the basis of the formation of a noncovalent inclusion complex through crown ether-ammonium ion interaction, a new ligand, 18-crown-6-aminoethanethiol (18C6-AET), was predesigned and synthesized with a formation constant of 4.26 x 10(2) M(-1)s(-1) for the 1:1 noncovalent complex. Consequently, stable crown ether-protected gold nanoclusters were synthesized with 18C6-AET in an aqueous medium with a rate of formation of 3.688 x 10(-4) min(-1). The newly formed 18C6-AET-capped gold nanoclusters showed quantized double-layer charging, revealing their concentric capacitor structure, and effective cluster capacitance, C(CLU) was calculated to be 0.93 aF from the single-electron events. A larger C(CLU) in comparison to that of monolayer-protected gold clusters with longer chain lengths was attributed to a smaller ligand shell thickness as well as the cationic nature of the nanoclusters formed in an aqueous electrolyte medium.