New insights on the Chemical Stability of Curcumin in Aqueous Media at Different pH: Influence of the Experimental Conditions

摘要

From spectrophotometric and electrochemical measurements recorded in curcumin aqueous solutionsat different pH values, both the stability and the acidity constants of curcumin were evaluated. It wasfound that contrary to hitherto acceptances, curcumin becomes stable at basic pH values while at acidones curcumin rate of degradation is around 20 times higher than in neutral or basic conditions.Notwithstanding, by controlling the experimental conditions the degradation rate of curcumin can bediminished even at acid and neutral conditions. Our results show that curcumin has 3 pKa values,namely: 7.428 ± 0.015, 9.552 ± 0.024 and 10.946 ± 0.034, and for the first time, the molar absorptivitycoefficients of the curcumin species in aqueous media: H 3 Cur, H 2 Cur ? , HCur 2? and Cur 3? , werereported as a function of the wavelength.