Kinetic Analysis of Hydrolytic Decomposition of Rubrocurcumin Analogues

Rubrocurcumin, the spiroborate complex of curcumin and oxalic acid, is classically used in the microscale estimation of boron in soil and plant samples. However, alternate methods are suggested due to its low hydrolytic stability in water-mediated conditions. For hydrolysis, the precursors for the preparation of the complex-curcumin, oxalic acid and boric acid, are generated and thus can be used for the release of curcumin, the super antioxidant. The decomposition kinetics of rubrocurcumin and its analogues were studied in the aqueousorganic medium at different temperatures and pH values by monitoring the absorption peaks of the complex at its wavelength maxima. The decomposition products were identified using UV-Vis and 11B NMR spectroscopy. The hydrolysis reaction was catalyzed by OH- ions and our results showed that these complexes were more stable at lower pH. A plausible mechanism for the hydrolysis of rubrocurcumin is proposed.