The binding free energy of complex [Co(C2O4)(3)](3-) to three peptides H-Lys-Gly-Lys-Gly-Lys-Gly-Lys-NH2 (P-1), H-(Lys-Gly-Lys-Gly-Lys-Gly-LyS)(2)-NH2 (P-2), H-(Lys-Gly-Lys-Gly-Lys-Gly-LyS)(3)-NH2 (P-3) and to the monomers (amino acids) forming the peptides has been obtained using the kinetics of the electron-transfer reaction between [Ru(NH3)(5)Py](2+) and [CO(C2O4)(3)](3-) as the probe. The polymerization of the monomers increases the negative free energy of binding and changes its character, noncooperative for the monomers and anticooperative for the peptides. This increase in the negative free energy represents a driving force for the polymerization process. The magnitude of the gain in negative free energy, as a consequence of the anticooperative character of the binding of the cobalt complex to the peptide, depends on the ratio of [complex]/[monomers].