Synthesis, characterization, and bioactivity evaluation of several divalent transition metal ion-bioflavonoid complexes

Interest in organic polyphenol compounds increases if these natural compounds are coordinated with transition metal ions. In this study, four metal complexes were synthesized with flavonoid extracts, and reliable techniques were used for characterization. These complexes showcase unique coloring, low pH, and conductivity levels, with X-ray diffraction revealing varying crystallinity among flavonoid extracts and certain complexes. Fourier transform infrared spectrophotometer exhibits a specific stretching vibration (442–486 cm−1 ν M−O), indicating flavonoid metal complex formation formation. UV–visible spectrum of flavonoid extracts displays absorption bands at 280 and 340 nm, shifting upon metal ion binding to unveil new absorption bands for each complex, producing three peaks between 260–660 nm. The 1HNMR results showed that the proton signals in all complexes shifted to a high field relative to their ligand, possibly due to increased coupling caused by the coordination effect and thus increased planarity of the flavonoid molecules. These organic metal complexes display heightened antioxidant, antimicrobial, and anticancer properties compared to extracts, with enhanced cytotoxicity against THP-1 and Calu-3 cell lines, notably Cu(II) displaying superior cytotoxic effects with IC50 values of 18 and 56 μg/mL for THP-1 and Calu-3 cells respectively.