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Int. J. Electrochem. Sci., 14 (2019) 5373 – 5385, doi: 10.20964/2019.06.24 International Journal of ELECTROCHEMICAL SCIENCE www.electrochemsci.org New insights on the Chemical Stability of Curcumin in Aqueous Media at Different pH: Influence of the Experimental Conditions J. Martínez-Guerra1, M. Palomar-Pardavé2,*, M. Romero-Romo2, S. Corona-Avendaño2, A. Rojas-Hernández1, M.T. Ramírez-Silva1,*, 1 Universidad Autónoma Metropolitana-Iztapalapa, Departamento de Química, Av. San Rafael Atlixco #186, Col. Vicentina, CDMX. C.P. 09340, México 2 Universidad Autónoma Metropolitana-Azcapotzalco, Departamento de Materiales, Av. San Pablo 180 Col. Reynosa-Tamaulipas, CDMX, C.P. 02200, México. *E-mail: mtrs218@xanum.uam.mx, mepp@correo.azc.uam.mx Received: 18 January 2019 / Accepted: 18 March 2019 / Published: 10 May 2019 From spectrophotometric and electrochemical measurements recorded in curcumin aqueous solutions at different pH values, both the stability and the acidity constants of curcumin were evaluated. It was found that contrary to hitherto acceptances, curcumin becomes stable at basic pH values while at acid ones 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 be diminished 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 absorptivity coefficients of the curcumin species in aqueous media: H3Cur, H2Cur−, HCur2− and Cur3−, were reported as a function of the wavelength. Keywords: Curcumin; stability; aqueous solution; pH; pKa 1. INTRODUCTION Curcumin [1,7-bis(4-hydroxy-3-methoxyphenyl)-1,6-heptadiene-3,5-dione] the main component of turmeric curcumin, also known as curcuma, is constituted by demethoxycurcumin, the bisdemethoxycurcumin and the cyclocurcumin. It is found in the roots of the Curcuma Longa L. plant [1]. The curcumin is a phenol compound with antiinflamatory [1, 2], anticarcinogenic [1, 3-5], antioxidant [1, 3, 6-8] and antiviral [9-13], properties that have been amply reported. Likewise, is used as coloring and spice in the textile and food industries [14], respectively. However, its low solubility in water gives rise to a low biodisponibility, which has hindered its potential application in thePDF Image | Curcumin in Aqueous Media at Different pH
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