Sequestration of biogenic amines by alginic and fulvic acids Original Research Article

The interaction of natural (alginic and fulvic acids) and synthetic (polyacrylic acid 2.0 kDa) polyelectrolytes with some protonated polyamines [diamines: ethylendiamine, 1,4-diaminobutane (or putrescine), 1,5-diaminopentane (or cadaverine); triamines: N-(3-aminopropyl)-1,4-diaminobutane (or spermidine), diethylenetriamine; tetramine: N,N′-bis(3-aminopropyl)-1,4-diaminobutane (or spermine); pentamine: tetraethylene-pentamine; hexamine: pentaethylenehexamine] was studied at T = 25 °C by potentiometry and calorimetry. Measurements were performed without supporting electrolyte, in order to avoid interference, and results were reported at I = 0 mol L− 1. For all the systems, the formation of (am)L2Hi species was found (am = amine; L = polyelectrolyte; i = 1…4, depending on the amine considered). The stability of polyanion–polyammonium cation complexes is always significant, and for high-charged polycations, we observe a stability comparable to that of strong metal complexes. For example, by considering the formation reaction (am)Hi + 2L = (am)L2Hi we found log Ki = 6.0, 6.5 and 10.8 for i = 1, 2 and 3, respectively, in the system alginate–spermidine. Low and positive formation ΔH° values indicate that the main contribution to the stability is entropic in nature. The sequestering ability of polyelectrolytes toward amines was modelled by a sigmoid Boltzman type equation. Some empirical relationships between stability, charges and ΔG° and TΔS° are reported. Mean values per salt bridge of formation thermodynamic parameters (ΔX°n) are ΔG°n = − 5.8 ± 0.4, ΔH°n = 0.7 ± 0.5 and TΔS°n = 6.5 ± 0.5 kJmol− 1 for all the systems studied in this work.