The ionic strength dependent binding mode of 9-aminoacridine (9AA), a
well-known DNA intercalator, to DNA is studied by flow linear dichrois
m, circular dichroism, fluorescence techniques and equilibrium dialysi
s. The DNA-bound 9AA exhibits spectral properties corresponding to the
intercalative binding mode disregarding the salt concentrations; the
angle between the long-axis transition moment of the 9AA molecule and
DNA helix axis is calculated to be about 65 degrees, indicating a sign
ificant deviation from the classical intercalation. At low salt concen
trations, however, upwards bending curve in Stern-Volmer plot is obser
ved (where 9AA is a fluorophore and DNA a quencher), indicating the co
existence of both static and dynamic quenching mechanisms or the exist
ence of an additional binding site.