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

Thermodynamic parameters for the interaction of protonated biogenic polyami nes 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 con stants and formation enthalpies were extrapolated to zero ionic strength. S pecies formed are ALH(r) [L = Cl-, SO42-, HPO42-, P2O74- and P3O105-; tartr ate, malate, citrate, glutamate, 1,2,3-propanetricarboxylate, 1,2,3,4-butan etetracarboxylate], with r = 1,2 ... (n + m - 2) and r = 1, 2 ... (n + m - 1) for inorganic and organic ligands, respectively (n, m = maximum degree o f protonation of amine and ligand, respectively). The stability of the vari ous species formed is a function of charges involved in the formation react ion. DeltaH(0) values are generally positive, and therefore these complexes are entropically stabilized. Results are discussed in connection with seve ral 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 a re reported. In particular, mean values of AGO and T DeltaS(0) for single i nteraction 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 o f inorganic and organic polyanions, respectively (n = number of possible sa lt bridges). A linear relationship was also found for T DeltaS(0) versus De ltaG(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 the rmodynamic parameters shows quite good predictive value. (C) 2001 Elsevier Science B.V. All rights reserved.