Synthesis of new anti-bacterial agents: Hydrazide Schiff bases of vanadium acetylacetonate complexes

Abstract

Four Schiff bases, L1, L2, L3 and L4 having –ON– donor system have been synthesised by the condensation of 4-(diethylamino)-2-hydroxybenzaldehyde with 4-nitrobenzohydrazide and 4-methoxybenzohydrazide to form L1 and L2. 4-(dimethylamino) benzaldehyde refluxed in the presence of 4-nitrobenzohydrazide and 4-methoxybenzohydrazide forms L3 and L4, respectively. The four Schiff base complexes (SBC 1A–1D) were synthesised by treatment of the Schiff base ligands with vanadium acetylacetonate and characterised using spectroscopic analysis such as FTIR revealing the presence of azomethine μ (C=N) stretching vibrations around 1612–1623 cm⁻¹, ¹H and ¹³C NMR revealing the presence of azomethine peaks to confirm the formation of the Schiff base ligands. The spectral data of the Schiff base complexes reveal the absence of the azomethine stretching vibrational frequencies and the presence of the V–O stretching vibrational frequency at 993 cm⁻¹. Thermal analysis of the ligands and complexes indicates high thermal stability of 280 and 160°C, respectively. Schiff base complexes 1A and 1B exhibited antimicrobial activities against both species tested with MIC of 305.3 and 378.9 mg/mL, these activities were dependent on the position of the hydroxyl and the length of the alkyl groups on the 4-Methoxy-benzoic acid (4-diethylamino-2-hydroxy-benzylidene)-hydrazide moiety of the Schiff bases complex.

Keywords:

• vanadium
• acetylacetonate
• FTIR
• thermogram
• Schiff bases complex
• azomethine and MIC

Public Interest Statement

The serendipitous discovery of an antitumor cisplatin’s complex there has been a paradigm shift in pharmaceutical and medicinal researchers. Since then, researchers have been poised in discovering novel metal complexes with medicinal properties to tackle infectious diseases. In this study, vanadium which is known to have moderate toxicity to man but found as a toxin in lower organisms was employed. The efficacy of the toxin against bacterial agents was modified by introducing ligand with activating or deactivating appendages. The minimum inhibitory concentrations and sensitivity of the Schiff base against clinical and resistance strains of Staphylococcus aureus and Enterococcus faecalis were of significance.

Presently, the pharmaceutical industries are finding a market for Schiff base complexes because economically, easy to synthesise the new anti-bacterial agents of vanadium hydrazide Schiff bases compared to the expensive synthetic route of other antibiotics. Scientifically, the interaction of the vanadium compounds with biomolecules is different when compared to other classic drugs.

Acknowledgement

We are thankful to Directorate of research, Vaal University of Technology, Vanderbijlpark, Gauteng, South Africa, for providing all necessary facilities to conduct the experiment.

Additional information

Notes on contributors

Bamidele Joseph Okoli

Our group interest in the synthesis of Schiff bases is motivated by the fact that Schiff bases are one of the important classes of organic compounds with a broad range of biological properties. They are often used as chelating ligands in the field of coordination chemistry, and when complexed with different metals, they exhibit a broad range of biological activities, including antifungal, antibacterial, antimalarial, antiproliferative, anti-inflammatory, antiviral and antipyretic properties. It is these potentials of the Schiff base that drives our research on developing antibacterial agents with novel and more efficient mechanisms of action since currently bacterium and fungi have developed resistance to the current line of treatment.