Anthraquinones quinizarin and danthron unwind negatively supercoiled DNA and lengthen linear DNA

•Anthraquinones quinizarin and danthron unwind negatively supercoiled DNA.•Anthraquinones quinizarin and danthron lengthen linear DNA.•Anthraquinones quinizarin and danthron possess middle binding affinity to DNA.•Anthraquinones quinizarin and danthron interact with DNA by intercalating mode. The intercalating drugs possess a planar aromatic chromophore unit by which they insert between DNA bases causing the distortion of classical B-DNA form. The planar tricyclic structure of anthraquinones belongs to the group of chromophore units and enables anthraquinones to bind to DNA by intercalating mode. The interactions of simple derivatives of anthraquinone, quinizarin (1,4-dihydroxyanthraquinone) and danthron (1,8-dihydroxyanthraquinone), with negatively supercoiled and linear DNA were investigated using a combination of the electrophoretic methods, fluorescence spectrophotometry and single molecule technique an atomic force microscopy. The detection of the topological change of negatively supercoiled plasmid DNA, unwinding of negatively supercoiled DNA, corresponding to appearance of DNA topoisomers with the low superhelicity and an increase of the contour length of linear DNA in the presence of quinizarin and danthron indicate the binding of both anthraquinones to DNA by intercalating mode.