This paper shows an in-depth study on the chemical and thermal responses of two ionic monolayer-protected gold clusters (Oct(4)N(+-)Br- and C OCt(4)N(+-)O(3)SS-IMPCs). Two IMPCs displayed completely different phase-transfer behaviors when the solutions were in contact with the aqueous solution containing N-(2-mercaptopropionyl)glycine (tiopronin). Not Oct(4)N(+-)O(3)SS-IMPCs but Oct(4)N(+-)Br-IMPCs experienced a facile phase transfer from the organic layer to the aqueous layer, which was resulted from the displacement of ionic ligands by tiopronin monolayers on the gold nanoparticle surface. When the toluene solution containing Oct4N+-Br-IMPCs was treated with the aqueous solution containing NaCl salts, the UV-vis spectrum of the solution containing Oct4N+-Br-IMPCs undertook a fast spectral evolution caused by decomposition/agglomeration of IMPCs. In contrast, Oct(4)N+-O3SS-IMPCs exhibited much higher stability against the NaCl treatments. The Oct(4)N+-O3SS-IMPCs also displayed a superior thermal stability at relatively high temperature of similar to 110 degrees C. Core size evolutions Of Oct(4)N(+-)O(3)SS-IMPCS without a fast decomposition or aggregation of clusters were also observed during solid-state heating treatments at similar to 150 and similar to 200 degrees C. These results support that the presence of different anions clearly affect the overall stability of ionic nanoparticles. The stronger binding property of thiosulfate anions compared to bromide anions with gold nanoparticle surfaces makes Oct(4)N(+-)O(3)SS-IMPCs chemically more inert and thermally more stable. (C) 2007 Elsevier Inc. All rights reserved.