Complexation of caffeic and ferulic acids by transition-metal ions

Potentiometric titration and IR and UV spectroscopies are used to study complexation of caffeic and ferulic acids by metal ions. Caffeic and ferulic acids, which occur in lignin, are shown to react with metal ions mainly through an ionic mechanism. However, coordination bonding is also possible depending oil the nature of the ligand and metal ion and the ratio of starting components. The strongest complex forms between caffeic acid and CuCl2 (2:1 ratio).