Reduction and subsequent aggregation of silver ions in the presence of various chelating agents such as trans-1,2-diaminocyclohexanetetra-acetic acid (DCTA) 1,2-propylenediaminetetraccetic acid (PDTA), diethylenetriaminepentaacetic acid (DTPA), and triethylenetetraamine-hexaacetic acid (TTHA) have been studied by pulse radiolysis. Rate constants of formation and transient absorption spectra for the ligand complexed Ag-0 and Ag-2(+) have been determined. The redox potential of Ag+(L)/Ag-0(L) becomes more negative than that of Ag+/Ag-0. Growth and reactivity of silver clusters were also studied in the presence of methyl viologen (MV2+). The kinetics of formation of the MV+circle radical, produced by the same pulse as in the case of silver atoms, confirms the catalytic electron transfer toward super critical silver clusters in the presence of ligands. The results suggest that catalytic electron transfer activity of silver clusters depends on the ligand. (C) 2003 Elsevier Inc. All rights reserved.