The process *Ru(bpy)(3)(2+) + S2O82- in two different reaction media, the SB4.5G dendrimer and DNA Solutions, was studied. In both media, the receptors have anionic characteristics. This fact will produce a binding of the ruthenium complex to the two receptors by attractive electrostatic interactions. On the contrary, the peroxodisulfate ions will be preferentially located in the aqueous solution due to electrostatic repulsions with the receptors. Despite the similarities of the receptors, some differences are observed in these two reaction media. These differences arise from the fact that the binding of the *Ru(bpy)(3)(2+) complex to DNA shows a negative cooperativity, whereas the binding to the dendrimer is noncooperative in character. The anticooperative character of the binding that happens in DNA Solutions becomes noncooperative when all electrolyte. NaNO3, is added to the medium. This is related to a condensation of the salt's counterions oil the Surface of the DNA which produces a decrease of the equilibrium constant corresponding to the binding of the complex to the receptor. Therefore, it is shown that the ionic strength of the reaction medium exerts a great influence Oil the cooperative nature of the ligand/receptor binding. This also explains the different behavior observed ill DNA and dendrimer solutions.