Voltammetric studies of the interaction of quinacrine with DNA.

The binding interaction of the antimalarial drug quinacrine with herring sperm deoxyribonucleic acid (DNA) has been studied by square wave voltammetry. The binding parameters, the binding constant K and the binding site size s, were obtained simultaneously by the analysis of bound and free quinacrine concentration corresponding to the limits of slow and fast binding kinetics compared to the experimental timescale. The binding constant and the binding site size for the interaction of quinacrine with DNA were K = 1.59 (+/-0.18)x10(5) M(-1) and s = 7.1 (+/-0.15) base pairs and K = 7.35 (+/-0.83)x10(5) M(-1), s = 6.2 (+/-0.02) base pairs for the limiting conditions of static and mobile binding equilibrium respectively. The standard Gibbs free energy change (Delta G0 = - RT ln K) is approximately -29.67 kJ/mol at 25 degrees C, which highlights the spontaneity of the binding of quinacrine with DNA. The binding of quinacrine to herring sperm DNA results in peak potential shifts in voltammetric and a red shift in UV-absorption measurements. The ionic strength dependence of the binding constant is not large. Furthermore, the relative viscosity of DNA increases in the presence of quinacrine. These characteristics strongly support the intercalation of quinacrine into DNA. The results also show that the intercalation of quinacrine into DNA may occur at approximately every seventh base pair.