Real-time detection of DNA cleavage induced by [M(2,2′-bipyridine) ₂(NO₃)](NO₃) (M = Cu(II), Zn(II) and Cd(II)) complexes using linear dichroism technique

The catalytic effect of [M(2,2′-bipyridine)₂(NO ₃)](NO₃) (M(bpy)₂, M = Cu(II), Zn(II) and Cd(II)) on the super-coiled and double stranded DNA (scDNA and dsDNA) was examined by electrophoresis and a real-time detection linear dichroism (LD) technique. Although the Cu(bpy)₂ complex effectively cleaved both types of DNA, the other two complexes were inactive. This was explained by the electrochemical properties of the metal complexes. The Cu(bpy)₂ complex exhibited a redox potential at - 0.222 V with a peak to peak separation of 0.201 V, whereas the other two metal complexes did not undergo any redox reaction. Both electrophoresis and LD measurements revealed the superoxide radical, ·O₂^-, to be responsible for DNA cleavage. A kinetic study using the LD technique showed that the cleavage of dsDNA consisted of two first order reactions. The fast reaction is believed to reflect the cleavage of one strand, whereas the slow reaction involves the cleavage of the complementary strand at or near the first cleaved site.