Abstract
Some novel (phenyl-diazenyl)phenols (4a–m) were designed and synthesized to be evaluated for their antibacterial activity. Starting from an active previously-synthesized azobenzene chosen as lead compound, we introduced some modifications and optimization of the structure, in order to improve solubility and drug conveyance. Structures of all newly-synthesized compounds were confirmed by 1H nuclear magnetic resonance (NMR), mass spectrometry, and UV-Vis spectroscopy. Antibacterial activity of the new compounds was tested with the dilution method against the bacteria strains Listeria monocytogenes, Staphylococcus aureus, Escherichia coli, and Pseudomonas aeruginosa PAO1. All the compounds were selectively active against Gram-positive bacteria. In particular, compounds 4d, 4h, and 4i showed the highest activity against S. aureus and Listeria monocytogenes, reaching remarkable MIC100 values of 4 μg/mL and 8 μg/mL. The relationship between antimicrobial activity and compound structure has suggested that the presence of hydroxyl groups seems to be essential for antimicrobial activity of phenolic compounds.
Highlights
Substituted azobenzene generally have a color ranging from yellow to red, due to the extensive conjugated system and presence of various electron-withdrawing or electron-donating substituents on the aromatic rings
20 μg/mL, the Minimum Inhibitory Concentration required to inhibit the growth of 100% of bacteria), against Candida albicans (MIC0 17 μg/mL, the Minimum Inhibitory Concentration required to inhibit the growth of 100% of fungi), and Listeria monocytogenes (MIC100 25 μg/mL) [16]
The MIC100 of all synthesized compounds was determined by the microbroth dilution method for Staphylococcus aureus ATCC 29213, a Listeria monocytogenes clinical strain, Pseudomonas aeruginosa PAO1, and Escherichia coli MG1655 reference strains (Table 2)
Summary
Substituted azobenzene generally have a color ranging from yellow to red, due to the extensive conjugated system and presence of various electron-withdrawing or electron-donating substituents on the aromatic rings. A key feature of azobenzene and other molecules characterized by a high conjugated pattern is its ability to absorb light with a consequent modification of its structure through the transition from cis isomeric form to the trans form This feature is widely-used in light-responsive materials [1,2,3,4,5], liquid crystals [6,7], electronic devices [8,9,10,11], or in NLO chromophores [12,13]. 4l), a tendency to crystallize from aqueous solution aqueous solution was observed during the period of incubation, and in these cases, it waswas not observed during period of incubation, and in these it was notFor possible to reach high possible to reach high the concentration of active molecule in thecases, dilution tests.
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