Interaction of Polyamines with Mg2+ and Ca2+

The interaction of some polyamines (ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, and spermine) with Ca 2+ and Mg 2+ has been studied potentiometrically at different ionic strengths (0.03 ≤ I /mol dm - 3 ≤ 0.96; 0.01 ≤ C CaCl 2 /mol dm - 3 ≤ 0.32; 0.01 ≤ C MgCl 2 /mol dm - 3 ≤ 0.32), at t = 25 °C. Experimental data have been interpreted in terms of both M 2+ −polyamine complexation and specific interaction (using Pitzer equations). For all the M 2+ −polyamine systems, MAH i ( i +2)+ species ( i = 0, 1, ..., n − 1; n = maximum degree of protonation of polyamine A) are formed, generally in the order Mg 2+ > Ca 2+ . For spermine and tetraethylenepentamine a binuclear species is also formed. By using the Pitzer specific interaction approach, we determined β (0), β (1), C ( φ ), and ϑ coefficients. The two approaches have been compared, and general equations for stability constants and interaction coefficients, which are valid for all the polyamines studied, are reported.