Abstract
The interactions of Fe(3+) with some ligands (Tranexamic (TXA(-)), Indole-3-acetic (IAA(-)), and Aminomethylphosphonic (AMPA(2-)) acids) of biological and environmental interest were studied. The speciation studies were performed in NaNO(3(aq)) and NaCl((aq)) using potentiometric and, only for IAA(-), spectrophotometric titrations at T = 298.15 K and 0.01 ≤ I/mol dm(-3) ≤ 1.0. The proposed speciation models are as follows: Fe(TXA)H(3+), Fe(TXA)(2)(+), Fe(TXA)(OH)(+), and Fe(TXA)(OH)(2(aq)) for TXA(-); Fe(IAA)(2+) for IAA(-); and Fe(AMPA)H(2)(3+), Fe(AMPA)H(2+), and Fe(AMPA)(+) for AMPA(2-). A comparison of logβ for the common FeL species gives logβ(FeIAA) = 6.56 and logβ(FeAMPA) = 14.84 (at I = 1.00 mol dm(-3) and T = 298.15 K), suggesting that AMPA(2-) has a higher complexing ability towards Fe(3+) than IAA(-). The dependence on the ionic strength of the formation constants was modeled by means of a Debye-Hückel type equation and the SIT model, whilst the sequestering ability of the investigated ligands towards Fe(3+) was quantified at various pHs, ionic strengths, and in the different supporting electrolytes by means of an empirical pL(0.5) parameter. To complete this study of the behavior of the different Fe(3+)/ligand systems, various simulations in biological fluids and natural waters were conducted.