Complexation equilibria and evaluation of thermodynamic parameters of bivalent metal complexes of glutathione

Abstract

Stability constants and themodynamic parameters (Δ<i>G, </i>Δ<i>H </i>and Δ<i>S</i>)<i> </i>of complexes of glutathione (GSH) with Cu(II), Pb(II),<i> </i>Ni (II), Zn(II), Co(II), Cd(II), Mn(II), Mg(II) and Ca(II) have been<i> </i>determined in aqueous medium <i>p</i>H-metrically at different ionic<i> </i>strengths and temperatures. The formation constants (log βn) have<i> </i>been calculated using the weighted least-squares method. The<i> </i>order of stability constant of the metal complexes of glutathione

has been found to be Cu(II) > Pb(II) > Ni(II) > Zn(II) > Co(II) >Cd(II) > Mn(II) > Mg(II) > Ca(II). Species distribution curves of complexes have been plotted as a function of <i>p</i>H which shows that complex formation starts at <i>p</i>H - 3.30 and becomes maximum at <i>p</i>H range 3.40-3.50 and after that it decreases to zero

concentration in the <i>p</i>H range 11.0-12.0.