Tetracoordinated ONNO donor purine-based Schiff base and its metal complexes: Synthesis, characterization, DNA binding, theoretical studies, and bioactivities

Tetracoordinated ONNO purine-based novel Schiff base (1) and its metal complexes Co(II), Ni(II), Cu(II), and Zn(II) (2-5) were procured from 2,6-diaminopurine and 5-chlorosalicylaldehyde and characterized by elemental analyses, IR, UV-Vis, magnetic measurements, ESI-MS, H-1 NMR, and C-13 NMR analysis. The new complexes showed an interesting structural variation: Distorted tetrahedral (CoL, CuL, and ZnL) and tetrahedral (NiL) geometries indicate that the metal ions bind with ligands through ONNO coordination sites. Density functional theory (DFT) and neutral bond orbital (NBO) calculations were performed to obtain an understanding of the structural characteristics, orbital interactions, and electronic chemical descriptors evaluation. Absorption and fluorescence spectra have been employed to examine the calf thymus deoxyribonucleic acid (CT-DNA)-binding behavior of the ligand and its complexes. Pharmacological activities, including in vitro antioxidant, in vitro anti-inflammatory, and in vitro antidiabetic assays, were performed. All compounds showed better activities compared with the free ligand. For anti-inflammatory and antidiabetic assays, ZnL complex showed high activity, whereas CuL complex exhibited the highest antioxidant activity among other metal complexes. Moreover, the zone of inhibition (ZOI) and minimum inhibitory concentration (MIC) of the synthesized compounds were screened for in vitro antibacterial activity against Staphylococcus aureus, Escherichia coli, Klebsiella pneumoniae, and Pseudomonas aeruginosa. Here also, complexes exhibited better antibacterial activity than the free ligand, especially the ZnL complex. The docking active site interactions were gauged to predict the activity of ligand and its metal complexes by binding with distinct active sites of B-DNA dodecamer (for DNA-binding activity), cyclooxygenase-2 (for anti-inflammatory assay), and alpha-amylase enzyme and alpha-glucosidase enzyme of human pancreatic system (for antidiabetic assay). The results indicated that the compounds are worth further investigation as a possible therapeutic agent.

Automated summary

A novel Schiff base compound and its metal complexes were synthesized and characterized. The complexes exhibited better antioxidant, anti-inflammatory, and antibacterial activities compared to the free ligand. The compounds showed potential as therapeutic agents.