Dipartimento di Chimica Inorganica, Chimica Analitica e Chimica Fisica, Università di Messina, Viale Ferdinando Stagno d'Alcontres 31, I-98166 Messina (Vill. S. Agata), Italy.
J Agric Food Chem. 2012 Aug 22;60(33):8075-82. doi: 10.1021/jf302007v. Epub 2012 Aug 7.
Quantitative parameters for the interactions between phytate (Phy) and Al(3+), Fe(3+), and Cr(3+) were determined potentiometrically in NaNO(3) aqueous solutions at I = 0.10 mol L(-1) and T = 298.15 K. Different complex species were found in a wide pH range. The various species are partially protonated, depending on the pH in which they are formed, and are indicated with the general formula MH(q)Phy (with 0 ≤ q ≤ 6). In all cases, the stability of the FeH(q)Phy species is several log K units higher than that of the analogous AlH(q)Phy and CrH(q)Phy species. For example, for the MH(2)Phy species, the stability trend is log K(2) = 15.81, 20.61, and 16.70 for Al(3+), Fe(3+), and Cr(3+), respectively. The sequestering ability of phytate toward the considered metal cations was evaluated by calculating the pL(0.5) values (i.e., the total ligand concentration necessary to bind 50% of the cation present in trace in solution) at different pH values. In general, phytate results in a quite good sequestering agent toward all three cations in the whole investigated pH range, but the order of pL(0.5) depends on it. For example, at pH 5.0 it is pL(0.5) = 5.33, 5.44, and 5.75 for Fe(3+), Cr(3+), and Al(3+), respectively (Fe(3+) < Cr(3+) < Al(3+)); at pH 7.4 it is pL(0.5) = 9.94, 9.23, and 8.71 (Al(3+) < Cr(3+) < Fe(3+)), whereas at pH 9.0 it is pL(0.5) = 10.42, 10.87, and 8.34 (Al(3+) < Fe(3+) < Cr(3+)). All of the pL(0.5) values, and therefore the sequestering ability, regularly increase with increasing pH, and the dependence of pL(0.5) on pH was modeled using some empirical equations.
在 298.15 K 下，在 I = 0.10 mol L(-1) 的 NaNO(3) 水溶液中，通过电位法确定植酸（Phy）与 Al(3+)、Fe(3+)和 Cr(3+)之间相互作用的定量参数。在很宽的 pH 范围内发现了不同的配合物物种。这些各种物种部分质子化，取决于它们形成的 pH 值，并以通式 MH(q)Phy（0 ≤ q ≤ 6）表示。在所有情况下，FeH(q)Phy 物种的稳定性比类似的 AlH(q)Phy 和 CrH(q)Phy 物种高几个对数单位。例如，对于 MH(2)Phy 物种，稳定性趋势为 log K(2) = 15.81、20.61 和 16.70，分别为 Al(3+)、Fe(3+)和 Cr(3+)。通过计算不同 pH 值下 pL(0.5) 值（即结合溶液中痕量存在的 50%阳离子所需的总配体浓度）来评估植酸对所考虑的金属阳离子的螯合能力。一般来说，在整个研究的 pH 范围内，植酸对所有三种阳离子都是一种相当好的螯合剂，但 pL(0.5) 的顺序取决于它。例如，在 pH 5.0 时，Fe(3+)、Cr(3+)和 Al(3+)的 pL(0.5) 分别为 5.33、5.44 和 5.75（Fe(3+) < Cr(3+) < Al(3+)）；在 pH 7.4 时，pL(0.5) 分别为 9.94、9.23 和 8.71（Al(3+) < Cr(3+) < Fe(3+)），而在 pH 9.0 时，pL(0.5) 分别为 10.42、10.87 和 8.34（Al(3+) < Fe(3+) < Cr(3+)）。所有的 pL(0.5) 值，因此螯合能力，随着 pH 的增加而规律增加，pL(0.5) 对 pH 的依赖性使用一些经验方程进行了建模。
