Polyfunctional Ligand of the Clinical Setting: Thermodynamic Studies of the Equilibria of Tranexamic Acid in Aqueous Solutions

Tranexamic acid (TXA) is the main component of antihemorrhagic drugs but is also used as an ingredient in cosmetic formulations for its depigmenting action. The acid–base properties were investigated in aqueous solutions containing NaCl, KCl, and (CH3)4NCl, at different ionic strengths, at T = 298.15 ± 0.15 K and only in NaCl(aq) at 283.15 ≤ T/K ≤ 318.15. The different behavior of TXA in the diverse media was explained by the formation of weak complexes with the components of the ionic media. The complexing ability of TXA toward Ca2+, Mg2+, Zn2+, and Sn2+, at T = 298.15 ± 0.15 K, was studied in NaCl(aq) in the range of 0.15 ≤ I/mol dm–3 ≤ 1.0; the modeling of the formation constants with ionic strength was performed by an extended Debye–Hückel type equation and the Specific ion Interaction Theory. For all M2+/TXA systems, the common M(TXA) species was obtained, and in the same experimental conditions, the stability trend observed is logKSnTXA > logKZnTXA > logKMgTXA > logKCaTXA. The sequestering ability of TXA toward the metals was estimated by means of pL0.5. To complete the picture of the chemical behavior of TXA, some simulations in blood plasma were also performed.