DNA binding and cleavage properties of a newly synthesised Ru(II)-polypyridyl complex

The single crystal X-ray structure of the newly synthesized ruthenium (II)-polypyridyl complex, [(bpy)₂Ru(L)](PF₆)₂ (1) (bpy is 2,2′-bipyridyl and L is 2-methyl-2H-1,3,7,8-tetraaza-cyclopenta[l]phenanthren-2-ol revealed a near planar conformation for the fused imidazole moiety, suggesting the complex may be capable of binding to duplex DNA. Binding-induced changes in spectral properties, along with thermal denaturation and viscosity measurement studies confirmed that the complex binds to CT-DNA with a moderately high binding constant value (4.1 × 10⁵ M⁻¹) through intercalation. Photocleavage studies with the pBR322 plasmid DNA were performed following excitation of this complex into the Ru(dπ) → bpy/L(π*)-based MLCT band and have shown that this complex cleaves the circular pBR322 DNA into linear DNA. Inhibitor studies revealed that the hydroxyl radicals were mainly responsible for the DNA photocleavage reaction. Preliminary studies indicate that the –OH functionality in 1 was also found to hydrolyse the phosphodiester linkage of pBR322 in the dark.