Varying structural motifs in the salen based metal complexes of Co(<scp>ii</scp>), Ni(<scp>ii</scp>) and Cu(<scp>ii</scp>): synthesis, crystal structures, molecular dynamics and biological activities

Abstract

Herein, we report the structural and biological activities of a deprotonated Schiff base ligand (H₂L) {H₂L = 1,1'-(1E,1'E)-(2,4,6-trimethyl-1,3-phenylene)bis(azan-1-yl-1-ylidene)bis(methan-1-yl-1-ylidene)dinaphthalen-2-ol} towards Co(ii), Ni(ii) and Cu(ii) complexes obtained under different conditions. Four new metal complexes have been synthesized: isostructural dimers [Co(L)]₂ (1)/[Cu(L)]₂ (3), a monomer (Cl₃NiH₂L)·(Et₃NH) (2) and a tetramer [Cu(L)]₄ (4). The bioactivity of 1-3 has been investigated through molecular docking with DNA and various proteins, known to be involved in the proliferation of viral diseases or progression of cancer. Complex 1 shows the best results, through a strong binding affinity with NS2B/NS3 protease (dengue virus) in terms of binding energy (-11.21 kcal mol^-1) and inhibition constant (6.02 nM). The experimental evidence for the effective binding of 1-4 with the Bovine Serum Albumin (BSA) protein and calf thymus DNA (CT-DNA) is in agreement with our molecular docking results. In addition, the cytotoxicity and antibacterial activity of 1-4 were examined and found to be compatible with biological systems, with 4 showing the highest antibacterial activity. All four complexes were analyzed by elemental analysis and UV/vis analysis, and their molecular structures were authenticated by single crystal X-ray studies.