Phase transfer of aqueous gold colloidal particles capped with inclusion complexes of cyclodextrin and alkanethiol molecules into chloroform

Colloidal gold particles synthesized in water have been capped with octadecanethiol (ODT) molecules rendered water-soluble by threading with α-cyclodextrin (α-CD) molecules. Thereafter, the gold nanoparticles could be transferred into an organic solvent such as chloroform by vigorous shaking of a biphasic mixture of the α-CD-threaded ODT-stabilized gold hydrosol and chloroform. The phase transfer of the gold nanoparticles could be observed as a rapid transfer of color from the aqueous phase to the organic phase. During shaking of the biphasic mixture, it is believed that α-CD molecules are dislodged from the octadecanethiol molecules, rendering the gold particles hydrophobic and amenable to phase transfer. Transmission electron microscopy studies of films of the gold nanoparticles in chloroform formed by solvent evaporation indicate a uniform size distribution of the nanoparticles and hexagonal close-packing of the particles in the film.