Two novel copper complexes of 2,2′-bipyridine: Evaluation of the DNA binding and cytotoxic activity

Two novel copper-2,2′-bipyridine complexes [Cu(SAL)(2,2′-bipy)ClO4]2 (1) and [Cu(μ2-O)(2,2′-bipy)NO3]2 (2) (HSAL = salicylaldehyde) were synthesized and characterized by X-ray single-crystal diffraction, elemental analysis and IR spectra. The interactions of the complexes with salmon sperm DNA were investigated by viscosity analysis, UV, fluorescence and circular dichroism (CD) spectroscopic techniques. Absorption spectral (Kb = 3.00 × 105 M−1 (1), 3.49 × 105 M−1(2)), emission spectral ((Ksv) 3.33 × 104 M−1 (1), 3.40 × 104 M−1 (2)), and viscosity measurements reveal that 1 and 2 interact with DNA through intercalation. In fluorimetric studies, the enthalpy (ΔH > 0) and entropy (ΔS > 0) changes of the reactions between the Cu (II) complexes with DNA demonstrate hydrophobic interactions. In addition, CD study indicates the Cu (II) complexes cause a more B-like to a more A-like conformational change upon binding DNA. All the experimental results show that the interaction mode of the two complexes was greatly affected by the coordination environments of Cu (II) centers. Their in vitro cytotoxicity towards five selected tumor cell lines HepG-2, HeLa, NCI-H460, MCF-7 and HL-60 has been evaluated by MTT method, and 2 exhibits higher growth inhibition of the selected cell lines at concentration of 50 μM, this result is identical with their DNA binding ability order.