Cyclic voltammetry was employed to investigate the extent of electrostatic binding for metal complexes such as ferrocyanide, [Fe(CN)(6)](4-), to full generations of polyamidoamine (PAMAM) dendrimers (G1.0-G5.0) as a function of size and pH. Addition of dendrimer solutions to metal complexes caused a large net positive shift in E-1/2 and reduced peak currents that varied with the size of the dendrimer. Binding ratios, K4-/K3-, calculated from the potential shifts changed from a ratio of five with small dendrimers (G1.0-G3.0) to 10 for G4.0 and G5.0, consistent with known structural changes in PAMAM dendrimers. Conditional binding constants for [Fe(CN)(6)](4-), calculated from the diffusion-limited oxidation currents, also increased from G3.0 (8.8 x 10(4) M-1) to G4.0 (31 x 10(4) M-1). At pH 5, the binding ratios increased dramatically at all generations, suggesting that the interior amine sites in the dendrimer are easily accessible to metal complexes and that dendrimers show some charge selectivity.