Bernabé-Pineda Margarita, Ramírez-Silva María Teresa, Romero-Romo Mario, González-Vergara Enrique, Rojas-Hernández Alberto
Departamento de Química, Universidad Autónoma Metropolitana-Iztapalapa, Area de Química Analítica, Apdo. Postal 55-534, C.P. 09340, México, D.F. México.
Spectrochim Acta A Mol Biomol Spectrosc. 2004 Apr;60(5):1091-7. doi: 10.1016/S1386-1425(03)00342-1.
The stability of curcumin (H3Cur) in aqueous media is improved when the systems in which it is present are at high pH values (higher than 11.7), fitting a model describable by a pseudo-zero order with a rate constant k' for the disappearance of the Cur3- species of 1.39 (10(-9)) Mmin(-1). There were three acidity constants measured for the curcumin as follows: pKA3 = 10.51 +/- 0.01 corresponding to the equilibrium HCur2- = Cur3- + H+, a pKA2 = 9.88 +/- 0.02 corresponding to the equilibrium H2Cur- = HCur-(2) + H+. These pKA values were attributed to the hydrogen of the phenol part of the curcumin, while the pKA1 = 8.38 +/- 0.04 corresponds to the equilibrium H3Cur = H2Cur- + H+ and is attributed the acetylacetone type group. Formation of quinoid structures play an important role in the tautomeric forms of the curcumin in aqueous media, which makes the experimental values differ from the theoretically calculated ones, depending on the conditions adopted in the study.
当姜黄素（H₃Cur）所处体系的pH值较高（高于11.7）时，其在水介质中的稳定性会提高，符合一个可用伪零级模型描述的情况，姜黄素Cur³⁻物种消失的速率常数k'为1.39×10⁻⁹ M·min⁻¹。测定了姜黄素的三个酸度常数如下：pKA₃ = 10.51 ± 0.01，对应于平衡HCur²⁻ = Cur³⁻ + H⁺；pKA₂ = 9.88 ± 0.02，对应于平衡H₂Cur⁻ = HCur²⁻ + H⁺。这些pKA值归因于姜黄素酚部分的氢，而pKA₁ = 8.38 ± 0.04对应于平衡H₃Cur = H₂Cur⁻ + H⁺，归因于乙酰丙酮型基团。醌型结构的形成在水介质中姜黄素的互变异构形式中起重要作用，这使得实验值与理论计算值不同，具体取决于研究中采用的条件。
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