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. On hydrolysis, the precursors for the preparation of the complex - curcumin, oxalic acid and boric acid are generated and thus can be used for curcumin release, the super antioxidant. The decomposition kinetics of rubrocurcumin and its analogues were studied in the aqueous-organic medium at different temperatures and pH by monitoring the complex absorption peaks at its wavelength maxima. The decomposition products were identified using UV-Visible and 11B NMR spectroscopy. The hydrolysis reaction was catalyzed by OH- ions and these complexes were more stable at lower pH. A plausible mechanism for the hydrolysis of rubrocurcumin is proposed.