Comparison and thermodynamic studies on complexation of adrenaline with some metal ions in mixed solvents

Abstract

Two methods are described for the determination of stability constants of adrenaline with metal ions. In method A, the solution equilibria of Al(III) complex formed with bidentate ligand of adrenaline in acidic media at pH ranges of ≈3 to ≈5 have been studied in cosolvent systems at 15, 20, 25±0.1°C and I=0.2 mol.dm-3 sodium chloride, employed phosphate buffer, with spectrophotometric methods. Evidence for the 2:1 complex was not observed for aluminum. The stability constants of the complex was determined and the resulting free-energy changes were obtained. The protonation constants of adrenaline were determined under the above condition. The results are discussed in terms of the effect of solvent on protonation and complexation. In method B, the complexation reaction with Fe(III) ions has been studied in water in 15, 20, 25±0.1°C. The stoichiometry of the complex was found to be 1:2 (metal ion/ligand). The stoichiometry of Fe(III)-adrenaline was estimated by mole ratio and continuous variation methods and emphasized by the KINFIT program. The values of the thermodynamic parameters for complexation reaction was obtained from the temperature dependence of the stability constants.