Spectro-electrochemical assessments of DNA/BSA interactions,cytotoxicity, radical scavenging and pharmacological implications of biosensitive and biologically active morpholine-based metal(ii) complexes: a combined experimental and computational investigation

Biosensitive and biologically active morpholine-based transition metal(ii) complexes (1–5) were constructed as [M^II(L) AcO]·nH₂O {where M = Cu (1) n = 1; Co (2), Mn (3), Ni (4), n = 4 and Zn (5) n = 2}, which were synthesized from 2-(-(2-morpholinoethylimino) methyl)-4-bromophenol ligand (HL) and structurally characterized by various analytical and spectroscopic techniques, which proposed a square planar and tetrahedral geometry around the central metal ion with lattice water molecules. The gel electrophoresis results revealed that complexes 1 and 5 had more potent DNA cleavage efficacy in the presence of an oxidizing agent (H₂O₂) as compared to the others. The observed DNA binding results for all the compounds as determined by spectro-electrochemical and hydrodynamic techniques were in the order 3.36 (1) > 3.06 (2) > 2.73 (4) > 2.61 (5) > 1.84 (3) > 1.00 (HL) × 10⁴ M⁻¹. The obtained bovine serum albumin (BSA) protein binding constant (K_b) results put forward the following order 2.38 (1) > 2.21 (2) > 2.18 (5) > 1.76 (4) > 1.40 (3) > 1.26 (HL) × 10⁴ M⁻¹. Also, the biothermodynamic parameters (, , ΔH° and ΔS°) and binding results divulged that all the complexes (1–5) could bind to DNA via intercalation in a spontaneous manner. Density functional theory calculations were employed to optimize the structure of ligand (HL) and its complexes (1–5) to gain insights into their electronic structures. Molecular docking analysis was carried out to identify the preferential binding modes of these complexes toward DNA and BSA protein. The theoretical observations of all cases were found to be very close to the experimental observations. Among the radical scavenging activity results for all the cases toward DPPH, hydroxyl radical, superoxide, nitric oxide and ferric reducing agents, complex (1) revealed a superior scavenging potency over the other compounds. In the screened antimicrobial reports against 10 different selected pathogenic species, although all the complexes (1–5) exhibited a greater significant inhibitory effect than the free ligand, complexes 4 and 5 achieved the best potency over standard drugs. The observed percentage of growth inhibition for all the compounds against the A549, HepG2, MCF-7 and NHDF cell lines suggested that complex 1 had enhanced growth-inhibitory potency over the other compounds and slightly affected normal cells as compared to the standard drug cisplatin, which may lead to its investigation as a promising anticancer agent in future research.

Morpholine-based metal(ii) complexes exhibited more significant biological activities than the free ligand. Among investigations towards DNA/BSA, the copper complex revealed excellent intercalating efficacy, which suggests it may have potential as a novel anticancer agent.