Interactions of acridine orange with nucleic acids. Properties of complexes of acridine orange with single stranded ribonucleic acid.

Interactions between acridine orange (AO) and nucleic acids (calf thymus DNA, and homoribo- and homodeoxyribo-polynucleotides) were studied in solutions containing ethanol as a cosolvent. Light absorption, scattering and luminescence were measured as a function of AO concentration at different dye/phosphate (D/P) ratios, and the data were analyzed using the McGhee-von Hippel probabilistic model of the polymer-ligand interactions. The absorption spectra of AO complexes with four homoribopolymers are presented. The intrinsic association constants and cooperativity coefficients of the formation of the complexes were calculated. The effects of ethanol (up to 35%, v/v) on these interactions were concentration dependent and may be extrapolated to zero concentration of this cosolvent. The possibility of destabilization of the double helix of nucleic acids by AO at high D/P ratios is discussed in light of the available thermodynamic data.