Study of Peculiarities of Differential Absorption Spectra of Complexes of Acridine Orange, Ethidium Bromide and Methylene Blue with Dna

Interaction of intercalators: ethidium bromide (EtBr), methylene blue (MB) and acridine orange (AO), with DNA at 0.02 M ionic strength of the solution has been studied by differential spectroscopy method. It was revealed that EtBr binds to DNA by intercalation, semi-intercalation and electrostatic modes; MB by semiintercalation and electrostatic modes and AO by intercalation and electrostatic modes. It was shown that the simultaneous performance of intercalation and semiintercalation modes condition the formation of a real isosbestic point (IP) in the spectra of EtBr–DNA complexes. In the absence of intercalation at MB interaction with DNA a pseudo-IP in differential absorption spectra of those complexes is formed. In the spectra of AO–DNA complexes both IP and pseudo-IP are not formed, despite the fact that this ligand binds to DNA by intercalation mode.