Thermodynamic parameters for the binding of inorganic and organic anions by biogenic polyammonium cations

Thermodynamic parameters for the interaction of protonated biogenic polyamines with inorganic or organic polyanions were studied potentiometrically (H+-glass electrode) and calorimetrically, at 25 degreesC. No background salt was used in the measurements to avoid interferences, and the formation constants and formation enthalpies were extrapolated to zero ionic strength. Species formed are ALH(r) [L = Cl-, SO42-, HPO42-, P2O74- and P3O105-; tartrate, malate, citrate, glutamate, 1,2,3-propanetricarboxylate, 1,2,3,4-butanetetracarboxylate], with r = 1,2 ... (n + m - 2) and r = 1, 2 ... (n + m - 1) for inorganic and organic ligands, respectively (n, m = maximum degree of protonation of amine and ligand, respectively). The stability of the various species formed is a function of charges involved in the formation reaction. DeltaH(0) values are generally positive, and therefore these complexes are entropically stabilized. Results are discussed in connection with several previously reported data on similar systems. DeltaG(0) and T DeltaS(0) follow a linear trend as a function of polyammonium cation and inorganic or carboxylic anion charges. DeltaG(0) and T DeltaS(0) charge relationships are reported. In particular, mean values of AGO and T DeltaS(0) for single interaction were calculated: DeltaG(0) = 7.0 kJ mol(-1) (n) under bar (-1), T DeltaS(0) = 9.1 kJ mol(-1) (n) under bar (-1) and DeltaG(0) = 5.7 kJ mol(-1) (n) under bar (-1) and T DeltaS(0) = 8.7 kJ mol(-1) n for the species of inorganic and organic polyanions, respectively (n = number of possible salt bridges). A linear relationship was also found for T DeltaS(0) versus DeltaG(0) whose equation is T DeltaS(0) = - 7-1.39 DeltaG(0) (with r = 0.9409; r, correlation coefficient). The body of correlations found for these thermodynamic parameters shows quite good predictive value.