Synthesis of water soluble copper(II) complexes: crystal structures,DNA binding,oxidative DNA cleavage,and in vitro anticancer studies

Two ternary copper(II) complexes of dl-threonine and polypyridyl ligands with formula of Cu(Thr)(Byp)Cl]·H₂O (1) and Cu(Thr)(Phen)H₂O]Cl·2H₂O (2) were synthesized. The complexes were characterized by spectral (NMR, FT-IR, and UV–Vis), CHN elemental analysis and have been structurally elucidated by X-ray crystallography. Both of the complexes formed slightly distorted square-pyramidal coordination geometry. The electronic absorption spectra of the complexes showed a very low intensity d–d electronic band in the range of 610–620 nm in Tris–HCl/NaCl (5:5 mM) pH 7.2 buffer solution. The DNA binding interaction with calf-thymus DNA (CT-DNA) was investigated by electronic absorption spectral titration and viscosity measurements. The results revealed that the phenanthroline complex (2) interact with CT-DNA through intercalation while bipyridyl complex (1) through the groove binding mode. The calculated intrinsic binding constant (K _b) of (1) and (2) were 0.5 and 4.4 × 10⁵ M^?1, respectively. Both the complexes were found to promote efficient DNA cleavage activities at low concentration in the presence of H₂O₂. The results showed that (2) has the highest DNA binding and nuclease activity. Furthermore, both the complexes were tested against human colon cancer (HCT 116) and breast cancer (MCF-7) cell lines and showed a dose-dependent antiproliferation effect.