Faculty of Science, Engineering and Technology (FSET)

Permanent URI for this communityhttps://repository.chuka.ac.ke/handle/123456789/156

Browse

Browsing Faculty of Science, Engineering and Technology (FSET) by Subject "Antibacterial activity"

Filter results by typing the first few letters
Now showing 1 - 1 of 1
  • Thumbnail Image
    Item
    Synthesis, characterization and antimicrobial properties of heterocyclic N, N’- bidentate ligands and their transition metal (ii) complexes
    (Chuka University, 2024) Otao Kevin Nyarango Otao
    Antimicrobial resistance has been named one of the greatest global threats to the health sector as many microbes are no longer susceptible to the drugs known to kill them, making diseases harder to treat or prevent. Efforts to develop new antibacterial agents with novel mechanisms of action, higher activity, and improved selectivity are crucial to address and counter antibiotic resistance. This study aimed at synthesizing and characterizing N, N’-bidentate ligands together with their copper and zinc complexes. The reaction of equimolar quantities of the selected hydrazinyl pyridazines with a diketone resulted in the formation of the expected pyrazolylpyridazines. The transition metal (II) complexes were obtained by the reaction of the metal chlorides with the synthesized ligands in the ratio 1:2. The synthesized ligands and the complexes were characterized using the melting point determination, molar conductivity measurements, FT-IR spectroscopy, UV-VIS spectroscopy, and 1H-NMR spectroscopy. The ligands melted at lower temperatures compared to the complexes (72, 141 and 148 °C for L1, L2 and L3 respectively). It was observed that the complexes decomposed in the range of 268-320 °C and that decomposition temperature was dependent on the increase in the molecular weights of the complexes. Conductivity measurements revealed that all the compounds are non-electrolytes with their conductivities in the range 8 - 20 Ω -1 cm2mol- 1. The spectral data revealed the presence of N, N’-donor groups in the aromatic rings due to the presence of –C=N- vibration bands at 1653cm-1, 1660 cm-1 and 1624 cm-1for L1, L2 and L3 respectively. Upon complexation, the bands shift to lower frequencies (1641, 1625 and 1598 cm-1 for zinc complexes of L1, L2 and L3 respectively, suggesting coordination through the N, N’-donor groups. An octahedral geometry of the complexes was proposed based on the presence of absorption bands in the wavelength range of 238 – 456 nm in the electronic spectra of the compounds. The 1H NMR revealed the presence of –C=N- with resonance peaks at ẟ = 8.2, 8.1 and 7.8 ppm for L1, L2 and L3 respectively. Upon complexation, these peaks shift downfield (8.44, 8.57 and 7.89 ppm respectively) indicating that coordination to the metal is exclusively through the N, N’ donor atoms in the ligands. Thereafter, the antimicrobial properties of the ligands and their corresponding complexes were tested using the disc diffusion method against the gram positive and gram negative bacterial strains (Escherichia coli and staphylococcus aureus) and the fungal strain (candida albicans). The diameter of inhibition was measured relative to that of the antibacterial standard (ampicillin) and the antifungal standard (fluconazole). Dimethyl sulfoxide was used as the negative control. The ligands L1, L2 and L3 had inhibition zones in the range 11-18 mm. for the complexes, inhibition zones were observed in the range 13-22 mm. The standards gave the highest inhibition zones in the range 22-28 mm. The evaluation results revealed that the transition metal (II) complexes exhibited higher antimicrobial activity than the free N, N’-donor bidentate ligands against the same bacterial strain. The increased activity of the complexes might be due to partial sharing of the positive charge of metal ion with the donor groups of the N, N’-donor bidentate ligand that increases the liposolubility of the complex across the microbial cell membrane. Based on the promising evaluation results, complexes in particular ZnL3 and CuL3 are recommended as lead compounds in the development of novel antimicrobials.