Synthesis, DNA binding, photo-induced DNA cleavage and cytotoxicity studies of europium(III) complexes

Two Eu(III) complexes, [Eu(acac)(3)(dpq)] (1) and [Eu(acac)(3)(dppz)] CH3OH (2) {viz. acetylacetonate (acac), dipyrido[3,2-d:20,30-f]quinoxaline (dpq), dipyrido[3,2-a:20,30-c] phenazine (dppz)}, have been synthesized and their DNA binding, photo-induced DNA cleavage activity and cell cytotoxicity are studied. The complexes display significant binding propensity to the calf thymus DNA in the order: 2(dppz) > 1(dpq). Cleavage experiments using pBR322 supercoiled DNA suggest major groove binding for 2 and minor groove binding for 1. The mechanistic aspects on natural light (natural light in room during the day) and UV-A (365 nm) irradiation are via a mechanistic pathway involving formation of singlet oxygen and hydroxyl radical as the reactive species. The photo-induced DNA cleavage activity of 2 is also stronger than 1. The cytotoxicity of 1 and 2 against HeLa (cervical) cancer cells show that the IC50 value of 19.11 +/- 3.56 mu M and 17.95 +/- 5.47 mu M, respectively.