Biol. Pharm. Bull. 27(5) 736—738 (2004)

the development of metal-based therapeutics. Cisplatin is one platinum complex and is widely used in treatments for cancer. Shimizu and Tsuji established a method of preparing colloidal platinum particles, whose average size is 2 nm, by ethanol reduction of H2PtCl6 in the absence of protective agents such as hydrophilic polymers. They used only the chemicals permitted to food additives such as ethanol and NaHCO3. The character of the suspension of colloidal platinum nanoparticles is shown in Table 1, and the solute of the suspension contains no salt because of low conductance. Platinum nanoparticles have negative surface potential from negative charges and are stably suspended from an electric repulsion between the same charged particles. Platinum is known to be used as a catalyst for a redox reaction, and Shimizu and Tsuji have studied whether this suspension of colloidal platinum nanoparticles have a reducing power for any oxides. The suspension of colloidal platinum nanoparticles reduced dark copper oxide on the surface of a cupper plate to glitter copper metal. Shimizu and Tsuji have been investigating the effect of the colloidal platinum for improving human health because of the reducing power of nanoparticles. In this study, we studied whether the reducing power of colloidal platinum nanoparticles is dependent on the action of the catalyst from a special property of platinum or on the transfer of electrons from charged platinum nanoparticles. It was shown that hydrogen peroxide, 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical and 2,6-dichlorophenol indophenol (DCIP) were reduced by colloidal platinum nanoparticles. This result is surprising in view of the fact that electrons of platinum nanoparticles can transfer to hydrogen peroxide, DPPH radical or DCIP.