Thermodynamic studies on complexation of divalent transition metal ions with some zwitterionic buffers for biochemical and physiological research

The interaction between the zwitterionic buffers (3-[N-bis(2-hydroxyethyl)amino]-2-hydroxy propane sulfonic acid, N-(2-actamido)-2-aminoethane sulfonic acid, and 3-[(1,1-dimethyl-2-hydroxyethyl)amino]-2-hydroxy propane sulfonic acid) with some divalent transition metal ions (CuII, NiII, CoII, ZnII, and MnII) were studied at different temperatures (298.15 to 328.15) K at ionic strength I = 0.1 mol · dm−3 NaNO3 and in the presence of 10%, 30%, and 50% (w/w) dioxene by using potentiometry. The thermodynamic stability constants were calculated as well as the free energy change for the 1:1 binary complexation. The protonation constants of the zwitterionic buffers were also determined potentiometrically under the above conditions.