Interaction between ethidium bromide and various polyelectrolytes and DNA with emphasis on spectral characteristics and binding curves of the bound dye.

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Visible and ultraviolet absorption spectra of ethidium bromide (EB) were measured by the optical titration method in the presence of each of three synthetic polyelectrolytes—sodium salts of poly(p-styrenesulfonate) (NaPSS), polyphosphate (NaPP), and polyacrylate (NaPA)—and native and heat-denatured DNA at 25 °C. By use of the principal component analysis (PCA) method, the number of EB species present in each EB–polymer system was determined to be two, i.e., free and bound EB, in the range of the polymer residue-to-EB ratio between zero and about one. The spectrum and the fraction of EB species bound to each polymer were determined by the extended PCA method. The bound-EB spectra are bathochromic and hypochromic relative to the spectrum of free EB, but they show no metachromasy band. The apparent binding constants Ka for EB bound to polymers are in the order of NaPSS>denatured DNA>NaPP>NaPA\fallingdotseqnative DNA.
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