Synthesis and characterization of hydrazones and their transition metal complexes: antimicrobial, antituberculosis and antioxidant activity

In the search of potential bioactive compounds, we have synthesized new Co(II), Ni(II), Cu(II) and Zn(II) metal complexes of hydrazone ligands derived by the condensation of benzyl carbazate with different derivatives of salicylaldehyde. Further, the synthesized compounds were precisely characterized by several physicochemical (TGA, powder XRD, SEM, EDAX) and spectroscopic techniques (FTIR, UV–Vis, NMR, mass spectrometry, ESR, fluorescence). Spectroscopic techniques proposed the octahedral geometry of the complexes coordinating via enolic oxygen atom, azomethine nitrogen atom, phenolic oxygen atom and oxygen atom of water molecules. The surface morphology of the ligands was distinct from metal complexes as revealed by SEM analysis. Further, serial dilution methodology was used to test the in vitro antimicrobial activity of the compounds (1–20) against four bacterial (E. coli, S. aureus, P. aeruginosa and B. subtilis) and two fungal (C. albicans and A. niger) pathogens and antituberculosis activity was assessed against M. tuberculosis H37RV (MTCC 200) strain using Lowenstein–Jensen (L. J.) slope technique while the DPPH assay was employed to examine the antioxidant activity of the synthesized compounds. The results of the pharmacological activities revealed that ligand H2L2 (2) and its Cu(II) and Zn(II) (11,12) complexes have potent antimicrobial and antitubercular activities while hydrazone ligand H2L4 (4) and its Cu(II) (19) complex show good efficiency for decolourizing purple colour of DPPH solution. In addition, in silico ADME study was conducted on the compounds which revealed that compounds have the potential to be administrated orally as active drugs.