Faculty of Science, Engineering and Technology (FSET)

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Browsing Faculty of Science, Engineering and Technology (FSET) by Subject "Antimicrobial resistance"

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    Green synthesis, characterization and antimicrobial activities of selected Schiff bases
    (Chuka University, 2024) Nyaga Jackline Njeri Nyaga
    Antimicrobial resistance is a serious global health challenge with alarming rates of emergence and spread of resistant microbes necessitating the development of novel antimicrobial agents. Schiff bases, also called imines or azomethines are synthesized from the condensation of aldehydes and amines. They have multiple properties including antibacterial and antifungal properties. Synthetic procedures of Schiff bases often involve the use of catalysts and solvents. The disposal of the latter, often leads to environmental pollution hence the need for the development of novel procedures that are applicable, environmentally friendly and economically realistic. Schiff bases were synthesized through grinding (for the solid aldehydes and amines) and stirring (for liquid aldehydes and amines) techniques without the use of catalysts and solvents in this work. This led to reduced reaction times, clean products, reduced possibility of pollution, no need for extra work up in the removal of solvents and catalysts and easy handling of the reagents. Six Schiff bases were synthesized. Schiff base S1, from benzaldehyde and 4-aminophenol, S2 from 4-aminophenol and 4-nitrobenzaldehyde, S3 from 4-aminophenol and salicylaldehyde, S4 from aniline and 4-nitrobenzaldehyde, S5 from aniline and salicylaldehyde and S6 from aniline and benzaldehyde. The compounds melted at constant temperatures demonstrating their purity. Characterization of the Schiff bases was done using FT-IR, UV-VIS and NMR (proton and carbon NMR) spectroscopy. Sharp IR peaks at 1628.95- 1617.38 cm-1 in the IR spectra of the compounds confirmed the formation of the imine bond, C=N. The disappearance of the carbonyl C=O peak at around 1600 cm-1 further confirmed the conversion of the aldehydes to imines. Free O-H broad bands were observed at 3447.91- 3339.29 cm-1. In compound S3, the O-H band was shallow and broad which was attributed to keto-enol tautomerism. In the UV-Vis spectra, bands at 261.40- 287.60 nm were observed corresponding to the n–π transitions of the azomethine C=N bond. NMR peaks at 7.26- 7.54 ppm for 1H NMR and 161.15- 158.34 ppm for 13C NMR further confirmed the presence of the imine protons and imine carbon atoms respectively. The disappearance of free NH2 peaks which usually occurs at 4.00- 6.00 ppm showed that the amines had been converted to imines. The synthesized compounds were subjected to antibacterial susceptibility tests against three Gram-negative bacteria (Pseudomonas aeruginosa, Escherichia coli and Salmonella typhi), one Gram-positive bacteria (Staphylococcus aureus) and one fungi Candida albicans at concentrations of 500 ppm, 250 ppm and 125 ppm. The zones of inhibition developed from 7.16- 20.00 mm on all the organisms at all concentrations indicating that all the compounds were biologically active. The data was analyzed using One- Way Anova. Significant difference between the means indicated that compounds with nitro and hydroxyl substitution had greater activity against gram negative bacteria while the compound lacking the substitution had better activity against gram positive bacteria. The compounds also showed better antifungal activity against Candida albicans than the positive control. This indicated that the compounds had great potential for development of antibacterial and antifungal drugs.
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    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.