The potentiometric determination of the formation constants of a novel class of macrocyclic polyaminocarboxylic acid ligands and the formation constants of the mercury(II)-glutathione complexes

Abstract

Potentiometric titrations were used to determine the thermodynamic formation constants of the complexes of newly synthesized macrocyclic polyaminocarboxylic acid ligands with selected metal ions. The formation constants were calculated with the help of a computer modeling program, BEST. Protonated complexes and hydroxylated complexes often coexist with the neutral complex in certain pH regions. This formation of multiple species is an important consideration in putting these ligands to practical use. It was also found that some of the complexes undergo a change in geometry when the pH of the solution is changed from acidic to basic. Electron spin resonance and UV-visible spectra confirmed these changes. The formation constants of the mercury(II)-glutathione complexes were also determined by potentiometric titrations. It was found that the previously reported value was incorrect by approximately ten orders of magnitude. The formation constants of the secondary species were also determined. These values have not been reported previously. A complete understanding of the solution chemistry of these complexes should be beneficial for understanding the metabolism of mercury(II) in living organisms.