Electrochemical and spectroscopic studies on the interaction of gallocyanine with DNA

The interaction of gallocyanine (GC) with double-stranded DNA (dsDNA) in pH 3.5 Tris-HCl buffer solution was investigated by electrochemical methods and spectrophotometric methods as well. In the potential scan range of -0.25 similar to +0.18 V (vs. SCE), GC had a couple of well-defined redox peaks at -0.022 V and -0.069 V on a cyclic voltammogram. at the scan rate of 100.0 mV/s, respectively. After the addition of dsDNA into the GC solution, the redox-peak currents decreased obviously and the peak potentials shifted positively. The results demonstrated that GC binding to DNA was caused by intercalation. Electrochemical parameters such as the electron number (n), the charge transfer coefficient (alpha) and the electrochemical reaction standard rate constant (k(s)) were calculated and compared in the absence and presence of dsDNA. Almost unchanged values of the electrochemical parameters after adding dsDNA showed that non-electroactive complexes were formed when GC interacted with DNA. The results indicated that the decrease of the redox-peak currents was caused by the decrease of the free concentration of GC in the reaction solution. The binding constant and binding ratio were investigated by spectrophotometric methods. DNA concentration can be determined by the decrease of the peak current of GC. The linear range for dsDNA was in the range of 1.45 X 10(-7)similar to 1.45 x 10(-6) mol/L and 1.45 x 10(-6) similar to 1.45 x 10(-5) mol/L, respectively, with the linear regression equation as Delta ip (10(-7) A) = 0.037 + 0.018C (10(-7) mol/L), and Delta ip (10(-7) A) = 0.25 + 0.041C (10(-6) mot/L), respectively, and the detection limit (3 sigma) was 1.13 x 10(-7) mol/L.