Synthesis and structure elucidation of new open cubane tetranuclear [CuII4] Cluster: Evaluation of the DNA/HSA interaction and pBR322 DNA cleavage pathway and cytotoxicity

Abstract

New open–cubane tetranuclear copper(II) complex of formulation {[Cu4(HL)4(H2O)2]·(CH3OH)2·(H2O)5}(1) derived from Schiff base ligand 2–((E)–(1,3–dihydroxy–2–methylpropan–2–ylimino)methyl)–6–methoxyphenol (HL) was synthesized. The characterization of both ligand (HL) and tetranuclear Cu complex was carried out by analytical, spectroscopic and single crystal X–ray diffraction. The structure analyses revealed that in the tetranuclear core, the metal centers are mutually interconnected via two phenoxo oxygen and two alkoxo oxygen atoms of four H2L2− ligand to generate a distorted single–open [Cu4(μ3–O)2]6+ open cubane core with the four Cu atoms disposed in an extended “butterfly–like” arrangement. Binding of complex 1 with CT DNA was investigated by using vivid spectroscopic techniques to study the mode of the interaction of 1 towards CT DNA. The results obtained indicated that 1 avidly binds to CT DNA via electrostatic mode with an intrinsic binding constant, Kb value 4.63×104M–1. Complex 1 showed an impressive nuclease activity generating single–strand breaks and the mechanistic investigation confirms the contribution of the reactive oxygen species (ROS). Likewise, the interaction of 1 with human serum album (HSA) revealed the change in intrinsic fluorescence intensity of HSA and was supposed to be associated with the microenvironment of Trp residue. Furthermore, the interaction of complex 1 with DNA and HSA was further investigated by the molecular docking studies which corroborated well with above findings. We have also tested 1 for cytotoxicity against the PC3 (Prostate) and K562 (Leukemia) cancer cell lines. The results exhibited were moderate when compared to standard drug viz, adriamycin (ADR).