Kinetic studies of the interaction of methyl orange with poly(L‐lysine) by stopped‐flow with circular dichroism detection

Abstract The interaction of methyl orange with poly( L ‐lysine) was studied kinetically by the stopped‐flow technique with CD detection, as well as by static CD titration experiments. In the static experiments, the differences observed in the polymer‐to‐dye ratio dependences of the CD spectra and absorption spectra suggested at least two kinds of bound states of the methyl orange attached to the polymer. The kinetic experiments using the stopped‐flow apparatus, however, revealed four distinct reaction processes. The reaction mechanism was elucidated from the concentration dependence of the time constant for each process as follows: the first process was attributed to the bimolecular binding step of methyl orange to the side chain of poly( L ‐lysine), the second and third process were ascribed to the intramolecular reaction of the polymer–dye complex, and the fourth process was found to be the intermolecular aggregation of the polymer–dye complex. The origin of the stacking of methyl orange on poly( L ‐lysine) is discussed on the basis of the characteristics of signal amplitudes obtained from the kinetic experiments for these processes.