Potentiometric and Electrochemical studies for the interaction of Zinc (II), Lead (II), Cadmium (II) with HEPES and HEPPSO as Zwitterionic Buffer Ligands at Different Temperature

Abstract

The complexation of the divalent transition metal ions Zn (II), Pb (II) or Cd (II) with two important biologically zwitterionic buffers (N-[2-hydroxyethyl] piperazine-N'-[2ethanesulfonic acid]) (HEPES) and (N-[2-hydroxyethyl] piperazine-N'-[2-hydroxypropanesulfonic acid]) (HEPPSO) in an aqueous medium, were studied using potentiometric pH titration in 1:1 ratio at four different temperatures 288 K, 298 K, 308 K and 318 K at ionic strength 0.1 molL-1 KNO3. The formation constants and thermodynamic parameters of different protonated, normal, monohydroxy and dihydroxy complexes for the binary systems M(II) + HEPES and M(II) + HEPPSO have been evaluated. The electrochemical behavior of the free Pb(II) and its binary complexes with HEPES and HEPPSO was studied by cyclic voltammetry on glassy carbon electrode. Upon temperature elevation the rate of the reduction process of the Pb 2+-HEPPSO is higher than that of Pb 2+-HEPES. The diffusion coefficient, the activation energies and the standard rate constant (Ks) for the diffusion process of Pb(II) complexes were calculated.