Chlorophyllin Competitive Effect on DNA-Binding Ligands

The effect of chlorophyllin on the binding of proflavine, doxorubicin, ethidium bromide, and berberine to DNA was studied by spectrophotometric titration. Titration data were analyzed using a multivariate curve resolution–alternating least squares method (MCR–ALS). Pure spectra of all absorbing species in the systems and their concentration profiles were obtained. Chlorophyllin was shown to form complexes with all studied ligands. The equilibrium constants for complexation of the ligands with chlorophyllin and DNA were obtained in binary (ligand–chlorophyllin and ligand–DNA) and ternary systems (ligand–chlorophyllin–DNA). The number of ligand molecules bound to DNA was observed to decrease in the presence of chlorophyllin. The main reason for this effect was heteroassociation because the calculated complexation constants of the ligands with DNA and chlorophyllin were similar. Theoretical isotherms of ligands binding to DNA in the ternary systems were compared to those obtained directly from decomposition data to test for the existence of other mechanisms for chlorophyllin competition. It was shown that consideration of only heteroassociation of the ligands with chlorophyllin (interceptor mechanism) was adequate to describe the experimental isotherms. Chlorophyllin did not exhibit protective properties in the studied ternary systems; consequently, chlorophyllin did not interact with DNA.