Synthesis of pyrimidine ligand and its mononuclear metal(II)/(III) complexes: Spectroscopic characterization, thermal, DFT, molecular docking, antimicrobial and anticancer studies

Mononuclear complexes of the type [M(L)2(H2O)2]Cl2 (where M = Co(II), Ni(II), Mn(II), Zn(II), Cu(II) and Cd(II)) and [Fe(L)2(H2O)2]Cl3 have been prepared and characterized by elemental, molar conductance, IR, electronic absorption, magnetic susceptibility, and thermal decomposition data. The identity and purity of the synthesized pyrimidine ligand (L) was confirmed by elemental analyses, IR, 1H NMR, and mass spectroscopy. The simultaneous (TG-DTG) study of metal complexes was found more thermally stable due to the 'structural complexity' at high temperatures. To support experimental findings, theoretical investigation of pyrimidine ligand (L) was performed with the DFT-B3LYP computational method. DFT calculations better understand molecular mechanisms that could not be elucidated experimentally. X-ray powder diffraction indicates that the Fe(III) complex is amorphous in nature, whereas the Cu(II), Co(II), Ni(II), and Mn(II) complexes have crystalline phases as well as the pyrimidine ligand. The SEM study revealed the nano size structure of Fe(III) and Ni(II) complexes. The interaction of the ligand with DNA was investigated by molecular docking studies, which indicated favorable docking in the minor groove of DNA of E. coli (3t88), S. aureus (3ty7), B. subtilis (5h67) and P. aeruginosa (5i39) receptors. The antibacterial and antifungal activity of the ligand and its metal complexes were found a very good potency when tested against multi-stranded microorganisms viz. Gram-negative bacteria (Escherichia coli, Klebsiella pneumonia and Pseudomonas aeruginosa), Gram-positive bacteria (Staphylococcus aureus and Staphylococcus mutans) and fungal species (Candida albicans and Aspergillus niger). All metal complexes exhibited more potential biological activity than free pyrimidine ligand (L) and may be used as antimicrobial agents. The cytotoxic activity against human liver (HepG2) and breast human (MCF-7) cancer cells were evaluated. All tested compounds showed potential anticancer activity, and the Cd(II) complex showed better activity results than the other tested compounds.