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

•Two new 2,2′-bipyridine-based binuclear Cu (II) complexes have been synthesized.•The binary complex shows stronger binding affinity to DNA.•The two complexes bind to DNA via intercalation.•Their in vitro cytotoxicity reflects their DNA binding strength order.•Thermodynamic parameters indicate that the binding reactions are hydrophobic.

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.

Graphical abstractTwo new copper(II) complexes containing 2,2′-bipyridine have been synthesized and fully characterized. DNA-binding study results prove that they interact with DNA through intercalation mode. The ternary complex 1 is a weaker intercalative candidate to insert into the DNA base pair compared with the binary one 2. And complex 2 exhibits higher growth inhibition of five selected tumour cell lines HepG-2, HeLa, NCI-H460, MCF-7 and HL-60.Figure optionsDownload full-size imageDownload as PowerPoint slide