Modified Flavonoids with Diamines and Polyamines Provide Enhanced Fluorescence and Antimicrobial Activity

Development of new biologically active materials based on natural products has, over the years, attracted considerable attention due to their effectiveness in human health and disease. Polyphenolic compounds, particularly flavonoids, provide a wide range of health benefits, including antioxidant, anti-inflammatory, anticancer, and antibacterial properties. A series of novel Schiff base derivatives of flavonoids with amino-containing linkers was successfully designed and synthesized through condensation reactions. Naringin and naringenin derivatives with diamines, including ethylenediamine (EDA), 1,3-diamino-2-propanol (DA-2-PrOH), tetramethylenediamine (TMEDA), pentamethylenediamine (PMEDA), as well as polyamines spermidine (SPD) and spermine (SPM), were synthesized and well-characterized through FT-IR, UV-Visible, ESI-MS, ¹H and ¹³C NMR spectroscopy, and elemental analysis. The so confirmed and well-characterized derivatives were subjected to photoluminescence studies, exhibiting enhanced activity, especially for naringin-based derivatives, and quenching in some others, thus verifying the significance of chemically modifying the conjugated systems of these molecules. Their biological activity was examined in the case of their antimicrobial efficacy against two Gram (+) (<i>Staphylococcus aureus</i> and <i>Bacillus cereus</i>) and two Gram (-) (<i>Escherichia coli</i> and <i>Xanthomonas campestris</i>) bacterial strains. Antibacterial screening projected selectivity of modified flavonoids against <i>E. coli</i>, proposing new "dense" flavonoid-(poly)amine materials as multifunctional antimicrobial agents and fluorescent probes.