Interaction of polyamines with Mg2+ and Ca2+

The interaction of some polyamines (ethylenediamine, diethylenetriamine, tr iethylenetetramine, tetraethylenepentamine, and Spermine) with Ca2+ and Mg2 + has been studied potentiometrically at-different ionic strengths (0.03 le ss than or equal to I/mol dm(-3) less than or equal to 0.96; 0.01 < C-CaCl2 /mol dm(-3) less than or equal to 0.32; 0.01 less than or equal to C-MgCl2/ mol dm(-3) less than or equal to 0.32), at t = 25 degrees C. Experimental d ata have been interpreted in terms of both M2+-polyamine complexation and s pecific interaction (using Pitzer equations). For all the M2+-polyamine sys tems? MAH(i)((i+2)+) species (i = 0, 1,.., n - 1; n = maximum degree of pro tonation of polyamine A) are formed, generally in the order Mg2+ > Ca2+. Fo r spermine and tetraethylenepentamine a binuclear species is also formed. B y using the Pitzer specific interaction approach, we determined beta((0)), beta((1)), C-(phi), and Theta coefficients. The two approaches have been co mpared, and general equations for stability constants and interaction coeff icients, which are valid for all the polyamines studied, are reported.