Thermodynamic Study on the Protonation and Complexation Epinephrine with Mg(II) in Mixed Solvent System and Various Ionic Strengths

Abstract

The complexation reactions between Mg²⁺ metal cation with epinephrine were studied in ethanol (ETOH)–water (H₂O) binary mixtures at different temperatures and different ionic strengths (0.2–0.6 mol dm^–3) using the spectrophotometric method. The pH-potentiometric titration method was applied for gathering experimental data and determination of solution equilibrium constant. The ionic strength affects proton-ligand stability constants and metal ligand stability constant. The stability constant of the complexes and the resulting free-energy changes are obtained. The protonation constants of epinephrine (using the potentiometric technique) and the stability constant of the complexes were determined at different temperatures and ionic strengths. The dependence on ionic strength of the protonation and stability constants was evaluated using a simple Debye–Huckel type equation The results show that the thermodynamic parameters are affected by the solvent percentage composition.