Electrochemical displacement method for the investigation of the binding interaction of polycyclic organic compounds with DNA.

The binding interaction of many organic carcinogens such as polycyclic aromatic hydrocarbons with DNA is the key step in their genotoxic effect. In this work, an electrochemical displacement method was developed to study such interaction. In the method, a DNA film is deposited on an indium tin oxide electrode surface by layer-by-layer assembly, and a redox-active DNA intercalator Ru(bpy) 2(dppz)(BF 4) 2 (bpy = 2,2'-bipyridine, dppz = dipyrido [3,2-a:2',3'-c] phenazine) is employed as an electrochemical indicator. If an organic compound competes with the indicator for the same binding site on DNA in the film, it would displace the ruthenium complex from DNA, resulting in a reduction in the measured electrochemical signal. From the titration curve, the binding constant of the organic compound with DNA can be calculated. With the use of oxalate as an electron donor to chemically amplify the oxidation current of the indicator, chemicals can be tested at low micromolar concentrations. Five well-known DNA binding polycyclic organic compounds, thiazole orange, 4,6-diamidine-2-phenylindole, H33258, ethidium bromide, and quinacrine, were investigated by the displacement method. The binding constants obtained in our experiments fall in the range of (4.3 x 10 (5)) to (1.2 x 10 (7)) M (-1), which are generally consistent with those reported in the literature by some established methods. The electrochemical method provides a general tool that complements the commonly used spectroscopic methods for the study of DNA/small molecule interactions.