Binding of 1,2,4-benzenetricarboxylate by open chain polyammonium cations

The interaction of some open chain polyammonium cations with 1,2,4-benzenet ricarboxylate was studied potentiometrically, at 25 degreesC. For all the i nvestigated systems, the species ALH(r)((r-3)) (r = 1,2...n+2; n = number o f aminogroups; A = amine; L = carboxylate) are formed. The stability of the se complexes depends on charges in the polyammonium cation and in the carbo xylic ligand, and for the reaction H(i)A(i+) + HjL(j-3) = ALH(i+j)((i+j-3)) we found a mean free energy contribution for salt bridge -DeltaG(0) = 6.5 +/-0.3 kJ mol (n) under bar (-1) ((n) under bar = number of possible salt b ridges). The results of this investigation are compared with those of simil ar systems. By considering also the tricarboxylic ligands citrate and 1,2,3 -propanetricarboxylate. we found for their complexes with polyammonium cati ons a fairly close stability. Calculations performed including complexes fo rmed with these two ligands give -DeltaG(0) = 6.6 +/-0.4 kJ mol(-1) (n) und er bar (-1) .