Synthesis and Characterisation of Azo Chromophores Tailored for their In vitro Antibacterial and Antioxidant Activities

Kai Wei, Yeo (2024) Synthesis and Characterisation of Azo Chromophores Tailored for their In vitro Antibacterial and Antioxidant Activities. Masters thesis, Universiti Malaysia Sarawak.

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Abstract

Non-communicable disease and bacterial resistance are complex combinations of problems that require immediate and effective alternatives. Concerning that, in this study, two series of azophenol derivatives 54a-m and 60a-m were successfully synthesised via diazo coupling reaction by employing 4-aminoacetanilide and p-toluidine, respectively as starting materials. Structural confirmation was done using CHNS elemental analysis, FTIR, 1H and 13C NMR spectroscopies. Both series were tested for antibacterial activities against Staphylococcus aureus and Escherichia coli as well as antioxidant activities employing DPPH and FRAP assays. The antibacterial study on 60a-m by Kirby-Bauer disc diffusion method showed poor inhibition towards both tested strains possibly due to the presence of amide moiety masked the cytoplasmic membrane depolarisation. In contrast, compounds 60a-m showed promising antibacterial activity portraying a better inhibition against S. aureus than E. coli potentially due to the difference in the cell wall structure with the latter being more complex. Further minimum inhibitory concentration (MIC) evaluation by turbidimetric kinetic method on 60a-m indicated that compound 60i (m-Br) resulted in a comparable MIC of 112.40 ppm (E. coli) and 103.95 ppm (S. aureus) with ampicillin 112.92 ppm (E. coli) and 95.70 ppm (S. aureus). This promising antibacterial activity of 60i (m-Br) was suggested due to its molecular size and polarisation ability leads to the formation of van der Waals interactions with the DNA of microbes. On the other hand, antioxidants evaluation on 54a-m and 60a-m by DPPH assay gave an IC25 in the range of 5.4 to 199.5 ppm as compared to ascorbic acid as standard at IC25 of 9.5ppm, while in FRAP assay gave a value of 12.29 to 210.95 mg Trolox Eq mg/ml with ascorbic acid gave 70.43 mg Trolox Eq mg/ml. Notably, the presence of the methoxy group in 60a-m enhances the antioxidant activities by increasing the electron cloud density of the benzene ring, especially when positioned at ortho- and para- of the hydroxyl group.

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