Chiral enantiomeric amino acid Schiff base copper(II) complexes 1 and 2 (a and b) were synthesized and characterized by various spectroscopic techniques (Fourier transform infrared, UV–vis, electron paramagnetic resonance, electrospray ionization-mass spectrometry, and circular dichroism) and single X-ray crystal diffraction analyses. To understand the selectivity and enantiomeric behavior of the complexes, binding interaction with ct-DNA and tRNA biomolecules was investigated by widely employed optical and hydrodynamic techniques. The binding experiments demonstrated that complexes 1 and 2 (a and b) interact strongly via the intercalative mode with preferential binding toward the tRNA biomolecule compared to ct-DNA. Furthermore, the order of binding propensity was 2a > 2b > 1a > 1b, implicating greater binding affinity of l-enantiomeric complexes, and complex 2a showed the highest binding propensity possessing a rigid aromatic group in the amino acid framework. Scanning electron microscopy analyses of complexes 1a and 2a revealed the formation of different morphologies with ct-DNA/tRNA molecules depending on the nature and extent of condensation induced by the complexes. The cleavage activities of complexes 1a and 2a showed a preferential oxidative cleavage mechanism toward the pBR322 plasmid DNA mediated by reactive oxygen species radical scavengers involving singlet oxygen (¹O₂) and superoxide anions (O₂^•–). The tRNA cleavage mechanism of complexes 1a and 2a revealed time- and concentration-dependent activities of these Schiff base Cu(II) complexes. In vitro cytotoxic activities of complexes 1 and 2 (a and b) revealed that among all, complex 2a showed the highest cytotoxicity, being selectively targeted toward the human breast cancer cell line (MCF-7) with a GI₅₀ value of <1 μM. The results suggest that the l-enantiomeric complexes are more avid binders toward the tRNA molecule and showed better cytotoxicity.

A new chromone-appended Cu(II) drug entity (1) was designed and synthesized as a potential anticancer chemotherapeutic agent. The structural elucidation was carried out thoroughly by elemental analysis, FT-IR, EPR, ESI-MS and single crystal X-ray crystallography. Complex 1 resulted from the in situ methoxylation reaction of the 3-formylchromone ligand and its subsequent complexation with the copper nitrate salt in a 2 : 1 ratio, respectively. 1 crystallized in the monoclinic P2₁/c space group possessing the lattice parameters, a = 8.75 Å, b = 5.07 Å, c = 26.22 Å, α = γ = 90°, β = 96.3° per unit cell. Furthermore, in vitro interaction studies of 1 with ct-DNA and tRNA were carried out which suggested more avid binding propensity towards the RNA target via intercalative mode, which was reflected from its K_b, K and K_sv values. The gel electrophoretic mobility assay was carried out on the pBR322 plasmid DNA substrate, to ascertain the cleaving ability and the mechanistic pathway in the presence of additives, and the results revealed the efficient cleaving ability of 1via the oxidative pathway. In vitro cell growth inhibition via the MTT assay was carried out to evaluate the cytotoxicity of complex 1 and IC₅₀ values were found to be in the range of 5–10 μg mL⁻¹ in HepG2 and MCF-7 cancer cell lines, which were found to be much lower than the IC₅₀ values of previously reported similar Cu(II) complexes. Additionally, in the presence of 1, reactive oxygen species (ROS) and thiobarbituric acid reactive substance (TBARS) levels in the tested cancer cell lines increased significantly, coupled with reduced glutathione (GSH) levels. Thus, our results suggested that ROS plays an important role in cell apoptosis induced by the Cu(II) complex 1 and validates its potential to act as a robust anticancer drug entity.