Synthesis, spectroscopic, and photophysical studies of Mn(II), Co(II), and Zn(II) complexes with 3-hydroxyflavone: Insights into anticancer activity against prostate cancer cells

This study reports the synthesis, spectroscopic and photophysical characterization, and anticancer evaluation of Mn(II), Co(II), and Zn(II) complexes with 3-hydroxyflavone. The complexes were obtained in a 1:2 metal-to-ligand molar ratio, yielding solid mononuclear species with the general formula ML₂·nH₂O, where M = Mn(II), Co(II), or Zn(II), and L⁻ = 3-hydroxyflavonate. The compounds were characterized by elemental analysis, thermogravimetric analysis (TG/DTG–DSC), differential scanning calorimetry, UV–Vis, FT-IR, NMR, ¹⁰⁹AgNP LDI MS (Fiber Laser-Generated Silver-109 Nanoparticles for Laser Desorption/Ionization Mass Spectrometry), and fluorescence spectroscopy. Spectroscopic studies indicated coordination through 3-hydroxy and carbonyl groups, leading to structural and electronic modifications of the ligand. Fluorescence properties were strongly influenced by metal coordination, with Zn–3-hydroxyflavone showing the most pronounced emission changes due to altered excited-state intramolecular proton transfer. The cytotoxic activity of the complexes was evaluated against prostate cancer (DU-145), normal prostate (RWPE-2), and normal fibroblast (BJ) cell lines. Zn–3-hydroxyflavone exhibited the highest anticancer activity, with a half-maximal inhibitory concentration (IC₅₀) of 4.08 μM. All complexes displayed selective cytotoxicity, as evidenced by the high viability of normal cell lines even at concentrations exceeding their IC₅₀ values. Recovery assays revealed either a permanent cytotoxic effect or partial regeneration of DU-145 cells following exposure to the complexes. Real-time detection of phosphatidylserine externalization, a key marker of apoptosis, indicated that induction of apoptosis is the most probable mechanism of action for the Mn(II) and Zn(II) complexes against prostate cancer cells.