Synthesis and structural elucidation of 1,2-naphthoquinone derivatives, Schiff base complexes and ternary complexes with 8-hydroxyquinoline: comparative studies of their antimicrobial, anti-inflammatory and anti-diabetic activities

Herein, a new derivative of 1,2-naphthoquinone with semicarbazide and its Schiff base complexes and ternary complexes have been synthesized with some transition metals such as Ni(II), Co(II) and Zn(II) by using the conventional reflux method and 8-hydroxyquinoline (8-HQ) as a secondary ligand for ternary complexes. All the compounds were characterized using elemental analysis, molar conductance, melting point, Powder XRD, magnetic moment measurement and various spectral techniques such as FTIR, 13 C NMR, 1 H NMR, and Mass Spectra. The specific peak of the enolic proton in 1 H NMR spectra of the tridentate ligand (L) explained the amido-iminol tautomerism in semicarbazone. In addition, powder XRD analysis and TGA confirmed the crystalline nature and the thermal study of metal chelates, respectively . In vitro , all the compounds were screened for antimicrobial (against bacterial strains: S. aureus and E. coli ; Fungal strain: A. niger ), anti-diabetic and anti-inflammatory activity with their obtained IC 50 values and compared with Acarbose and Aspirin standard drugs. Bioactivities of azomethine containing free ligand (L), their Schiff base complexes and ternary metal chelates were compared to each other. Free Schiff base (L) was found most potent for all selective bioactivities compared to their all-metal complexes, except Ni (II) Schiff base complex showed excellent activity against C. albicans.