Non-covalent DNA binding, protein interaction, DNA cleavage and cytotoxicity of [Cu(quamol)Cl]·H₂O

A copper(II) complex [Cu^II(quamol)Cl]·H₂O, where H(quamol) is N-2-(quinolyl-methylidene)aminophenol, has been isolated. The solution structure of the complex has been assessed to be distorted square-planar. The complex displays a ligand field band in the visible region (608nm) and also show axial EPR spectrum in DMF at 77K with g_||>g_⊥ indicating a d_x²_-y² ground state. The g_|| and A_|| values of 2.265 and 153×10^-4cm^-1, respectively, conform to a square-based CuN₂OCl chromophore. The interaction of the complex with calf thymus (CT) DNA has been explored by using absorption (K_b=2.48×10⁵M^-1), emission (K_app=7.72×10⁴M^-1) and circular dichroic (CD) spectral measurements, which reveals that a complex interacts strongly with DNA through partial intercalation. The electrochemical studies indicate that Cu(II) binds to DNA more strongly than Cu(I). It cleaves ϕX174 supercoiled phage DNA in the presence of ascorbic acid as a reducing agent. Meanwhile, the interaction of the complex with bovine serum albumin (BSA) indicates that the complex can markedly quench the intrinsic fluorescence of BSA via a static quenching process and cause its conformational change. Interestingly, the observed IC₅₀ values for the cell lines EVSA-T (breast cancer) and M19 MEL (melanoma) are in the range of those observed with cisplatin while M19 MEL cancer cell line, complex is more active than 5-fluorouracil. The complex is non-toxic to healthy cells.