The formation and stability of protonated diamines-carboxylic ligand complexes was studied potentiometrically (H+ -glass electrode). Species formed are ALH(r) (A = cadaverine, putrescine, L = acetate, malate, tartrate, malonate, citrate, 1,2,3-propanetricarboxylate, 1,2,3,4-butanetetracarboxylate and glutamate; r=l...m+1, where m is the maximum degree of protonation of the carboxylic ligand), and their stability is a function of charges involved in the formation reaction. For the equilibrium H(i)A(i+) + HjL(j-z) = ALH(i+j) ((i+j-z)) the following linear relationships can be written: log K-1j = - 0.25 + 0.75 \j- z\, log K-2j = 0.50 + 0.90 \j-z\ (by also considering some ethylenediamine and 1,2-diaminopropane complexes). Medium effects were considered. Comparison was made with analogous inorganic polyanion complexes. The simplest relationships -Delta G(0) = 6.5 +/- 0.3 and -Delta G(0) = 7.9 +/- 0.6 kJ mol(-1) n(-1) (n = number of possible salt bridges) were found for carboxylic and inorganic anions, respectively. (C) 1998 Elsevier Science B.V. All rights reserved.
