Research on the chelation between luteolin and Cr(III) ion through infrared spectroscopy, UV–vis spectrum and theoretical calculations

The chelation between luteolin and Cr(III) ion is studied using the theoretical methods. Many different potential complexes, formed with natural and deprotonated luteolin chelating bare and hydrated Cr(III) ion, respectively, are studied by using Density Functional Theory method. Both total and binding energies are calculated. The results from the studies indicate that Cr(III) ion is affine in forming a complex with luteolin at the 5-hydroxy-4-keto site and that deprotonated luteolin has stronger chelating power than natural luteolin. The reactivity differences between luteolin and luteolin–Cr(III) complexes are observed through comparison of their Conceptual DFT reactivity indices. Apart from the theoretical studies, the experiments are performed to modify the theoretical conclusions. Meanwhile, luteolin–Cr(III) complex has been synthesized, and the chelation site is analyzed using IR spectroscopy and UV/vis spectrum. The experimental results are found to have the same conclusions as those by theoretical studies.

► Cr(III) ion is inclined to chelate at 5-hydroxy-4-keto site of luteolin.
► The reactive activity of luteolin–Cr(III) complex is higher than that of luteolin.
► Luteolin and luteolin–Cr(III) complex have different nucleophilic region.