Synthesis, crystal structures, DNA/bovine serum albumin binding, DNA cleavage and cytotoxicity of five mononuclear zinc(II) complexes

Five new mononuclear zinc(II) complexes containing ligands with extended planar phenanthroline moieties (dipyrido-[3,2-a:2 ',3 '-c]phenazine (dppz) or dipyrido[3,2-d:2 ',3 '-f] quinoxaline (dpq)), namely [Zn(dppz)(acac)(2)]center dot CH3OH (1), [Zn(dppz)(dbm)(OAc)] (2), [Zn(dpq)(dbm) (OAc)] 1.5H(2)O (3), [Zn(dpq)(tfnb)(OAc)] (4) and [Zn(dpq)(tfnb)(2)] (5), where acac = acetylacetonate, tfnb = benzoyltrifluoroacetone and dbm = dibenzoylmethane, were synthesized and structurally characterized. The binding ability of complexes 1-5 with calf thymus DNA was investigated by spectroscopic titration methods and viscosity measurements. Results indicate that all complexes bind to calf thymus DNA via intercalative mode, and the DNA binding affinities of dppz complexes 1 and 2 are apparently stronger than those of dpq complexes 3-5. DNA photocleavage experiments reveal that these complexes are efficient DNA cleaving agents and they are more active in UV-A (365 nm) than in visible light. In particular, the in vitro cytotoxicity of the complexes for human cancer cell line A549 demonstrates that the five compounds have anticancer activity with low IC50 values. Meanwhile, interaction of the complexes with bovine serum albumin investigated using UV-visible and fluorescence methods indicates that all complexes can quench the intrinsic fluorescence of bovine serum albumin in a static quenching process.