Design, Spectroscopic Analysis, DFT Calculations, Catalytic Evaluation, and Comprehensive In Silico and In Vitro Bioactivity Studies, Including Molecular Docking, of Novel Co(II) Complexes of 2-Hydroxy-5,3-(phenylallylidene)aminobenzoic Acid

The main target of the current research is designing and synthesizing novel Co(II) complexes derived from 2-hydroxy-5,3-(phenylallylidene)aminobenzoic acid ligand and to enhance comprehension as potential photocatalyst, antibacterial, antifungal, and antioxidants alternatives by means of using density functional theory (DFT) calculations and molecular docking investigation. Thus, 2-hydroxy-5,3-(phenylallylidene)aminobenzoic acid (L1), was prepared by thermal condensation of cinnamaldehyde with 5-aminosalicylic acid in methanol. A series of cobalt(II) complexes with newly synthesized Schiff base ligand and para substituted phenylphenol (L2) corresponding to complex 1, [Co^II(L1)₂(H₂O)₄], and mixed-ligand complexes, 2 and 3, [Co^II(L2)_1/2(L1)(H₂O)_4/3], have been prepared and analysed by FTIR, ¹H NMR, HRMS, PXRD, electrochemical and fluorescence spectral techniques. DFT calculations were utilized to verify the molecular structure, analysis of Frontier Molecular orbitals (FMOs), molecular electrostatic potential (MEP) and reactivity descriptor for complexes 1–3. In vitro experiments were conducted to evaluate the biological properties of the complexes. These findings revealed that the synthesized metal complexes have heightened biological efficacy as related to the unbound ligand. Complex 2 has been observed to show effective antibacterial MIC value against P. aeruginosa (3.81 μg/mL) which is superior to the efficacy of standard drug chloramphenicol used (7.81 μg/mL) while the antifungal activity of complexes was found to be moderate to that of standard nystatin. Complex 2 has also demonstrated strong antioxidant activity (67.7%), which was on par with ascorbic acid used as a reference. Furthermore, in silico antibacterial activities (molecular docking) of the complexes have indicated these to exhibit excellent efficacy with docking score of − 11.1, − 9.8 and − 9.4 KCalmol⁻¹ against target proteins E. coli (PDB ID: 4OPQ), P. aeruginosa, (PDB ID: 6NE0) and S. aureus, (PDB ID: 3Q89), respectively. The photocatalytic behaviour of the Co(II) based complexes has been studied by Buchwald-Hartwig C–N (BHC) and Suzuki Miyura C–C (SMC) cross coupling reactions. Lastly, a correlation between in vitro efficacies with molecular docking data and photocatalytic activity with DFT data was done and analysed.

Graphical Abstract.