Zinc(II)‐N2O2 ligation complex‐based DNA/protein binder and cleaver having enhanced cytotoxic and phosphatase activity

Abstract

The alkyne arms containing zinc(II) N2O2 ligation complexes (1) and (2) were prepared from 2,2′‐{cyclohexane‐1,2‐diylbis[nitrilo(E)methylylidene]}bis[5‐(prop‐2‐yn‐1‐yloxy)phenol] (L1) and 2,2′‐{1,2‐phenylenebis[nitrilo(E)methylylidene]}bis[5‐(prop‐2‐yn‐1‐yloxy)phenol] (L2) and characterized by analytical and various spectral techniques. The molecular geometry of 1 and 2 was optimized by Density Functional Theory (DFT) at B3LYP/6‐311G(d,p) level and compared with literature. The complexes are stable in solution, and their solution structure was assessed using NMR and ESI‐MS spectroscopy. Topological analysis of the electron density and nature of the bonding in the complexes has been determined by using Bader's AIM method. The interaction and binding modes of calf thymus DNA (CT‐DNA) with complexes (1 and 2) were investigated by using absorption and emission spectral and viscometric studies. The nuclease activity investigated through gel electrophoresis reveals that 1 and 2 exhibits a significant DNA cleavage activity via a hydrolytic pathway and is further confirmed by an experiment performed in the presence of T4 ligase. The protein binding ability of 1 and 2 with bovine serum albumin (BSA) protein evaluated show good protein binding propensity. In‐vitro cytotoxicity of the complexes has shown significant activity against human brain tumor (U87 MG) and breast carcinoma (BT20) cancer cell lines. The comet assay has been used to determine the extent of DNA fragmentation in cancer cells. The phosphatase activity investigated through kinetic measurements establishes that the zinc complexes possess significant hydrolytic efficiency and follow the order 2 > 1. The DFT calculations have also been carried out to support the proposed mechanistic pathway of catalytic activity.