Complexation Equilibria of Zn(Ⅱ), Pb(Ⅱ) and Cd(Ⅱ) with Reduced Glutathione (GSH) and Biologically Important Zwitterionic Buffers

摘要

The interaction of zinc(Ⅱ), lead(Ⅱ), and cadmium(Ⅱ) with Glutathione (δ-L-glutamyl-Lcysteinylglycine) as primary ligand and zwitterionic buffers (N-[2-Hydroxyethyl]piperazine-N'-[2-ethanesulfonic acid]) (HEPES) and (N-Hydroxyethyl]piperazine-N'-[2-hydroxy-propanesulfonic acid]) (HEPPSO) as secondary ligands were studied by potentiometric-pH titration in 1:1:1 ratio at 25.0℃ and Ⅰ = 0.1 mol.dm~(-3)(KNO_3). The formation constants of different normal and protonated binary and ternary complex species were calculated. Formation constants for the monohydroxy, and dihydroxy complexes for the binary systems M(Ⅱ) + HEPES and M(Ⅱ) + HEPPSO have been evaluated. The distribution curves for the various complex species as a function of pH were constructed.