The study of the processes [Ru(NH3)(5)pz](2+) + S2O82- and [Fe(bpy)(3)](2+) + S2O82- (pz = pyrazine, bpy = 2,2'-bipyridine) was carried out in the presence of calf thymus DNA and hexadecyltrimethylammonium bromide (CTAB) as surfactant at different concentrations of polymer and surfactant. Results show a different kinetic behaviour depending on the molar relation [surfactant]/[DNA], that is, on the conformation of the polynucleotide. The conclusion obtained was that the cac value, that is, the surfactant concentration necessary to produce condensation of the DNA, can be estimated from kinetic data. In the authors' opinion, it is the first time that this type of study has been used to determine the conformation change of a polymer. (C) 2011 Elsevier B.V. All rights reserved.